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Diagnostics, tips, & tricks by Jim Levie (E30 Jedi Master)

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    Diagnostics, tips, & tricks by Jim Levie (E30 Jedi Master)

    Please don't add any replies as a moderator will have to clean those out after the thread is fully populated.

    This is a collection of all of the diagnostics, tips,and such that I've written (and pasted into threads many times). If I have errors, or have written things that need clarification, please let me know by a PM. If there are things that you'd like to see added, also let me know by a PM and I'll see what I can do. Most of what is here I wrote, but there are some things that I lifted from the Internet. Along the same lines, if you have something you'd like to discuss, on-line, start a thread in the General Maintenance forum and we can talk about it there.

    Also, if someone wants to contribute an article please contact me via PM. It will be published with acknowledgement of the source of the information.

    As some may know, I'm not into esthetic or stylistic subjects. But rather into making an E30 run right and perform well. While mainly aimed at cars with the M20B25 engine, a lot also pertains to other E30 variants.

    Some useful on-line resources are:

    Wiring diagrams:
    BMW Illustrated Parts Breakdowns:

    ABS Diagnostics
    Alternator Diagnostics and Battery Info
    Brake and Clutch Hydraulics
    Brake System Flush & Bleed
    Check Panel Brake Warning Light
    Cooling System Bleed Procedure
    Cooling System Flush Procedure
    Differential Rebuilding
    E30 Lubricants
    Engine Cleaning
    Engine Management Diagnostics
    Excessive Parasitic Draw
    Head Gasket Leak Diagnostic
    Intermediate Shaft Bearings
    M20B25 DME Diagnostics
    OBD-1 Diagnostics
    Parking Brake Adjustment
    Rear Drive Train and Driveshaft
    Scheduled Maintenance
    SI Board Battery Replacement
    Subframe Bushings
    Suspension Check
    TPS & Idle Adjustment
    Wheel Bearings

    Now for a couple of things to illustrate the diagnostic/repair difficulties one can run into. They are rather long, but you might find them to be an interesting read.

    Engine Management Saga
    Fuel Tank Saga

    I have several PDF files covering AFM testing/repair, replacement of the clutches in an LSD, and R134a retrofit that I shamelessly scarfed from the Internet. I can't post those in this thread, but I'll happily send you a copy if you will send me a PM with an email address. I also have a few links to articles in other forums (like an auto to manual swap). I don't like to post links to other forums, but if you will send me a PM with an email address I'll send you the link.
    Last edited by jlevie; 09-07-2015, 10:14 AM.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

    ABS Diagnostics

    The ABS system on an E30 is pretty simple. It consists of a wheel speed sensor at each wheel, and ABS module & relay above the steering column, and the ABS unit in the engine bay. It has no connections to any other parts of the car.

    If the ABS light comes on when the ignition is turned on and doesn’t go off when the engine starts the relay, module and unit are all suspect. There is a fusible link in the ABS relay that, if blown, will cause this. The fuse (a simple piece of wire) can be replaced, or better yet get a new relay. If that fails to solve the problem the ABS module or the ABS unit are the next suspects. The ABS unit contains relays that have been known to fail and can be replaced with OE parts. So you have two choices. replace the ABS module with a known good unit, or replace the relays or the entire ABS unit. I start with the ABS module.

    If the light comes on with ignition, goes out with engine start, and comes back on once the car starts moving, one (or more) of the wheel speed sensors is bad or the ABS module is bad. A simple test of the speed sensors is to disconnect all but one and see if the light comes on while driving. Since the ABS system only gets speed data from the wheel speed sensors, a good sensor will cause the light to come on as the module doesn’t see data from the other sensors. Repeat this test with each of the other speed sensors. A bad one will cause the light not to come back on as the ABS module can’t tell that the car is moving. Replace that sensor(s) and see what happens. It is possible that one or more of the input channels in the ABS module are bad.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL


      Alternator Diagnostics and Battery Info

      A simple DIY test of the alternator can be done with a DMM. At idle you should see about 13.5v and your should see about 14v at 2500rpm. The 2500rpm reading should not drop much if you load the system by turning on the headlights and the HVAC blower to high. If you don’t see those voltages the alternator isn’t working correctly.

      In many cases the cause will be worn brushes in the regulator/brush assembly. If the alternator bearings are in good condition a new regulator/brush assembly may be all that is needed.

      If you remove the alternator belt, you can check the condition of the bearings. But that isn't necessarily a conclusive test as the alternator bearings won't be under load. A simple DIY test of the alternator can be done with a DMM. At idle you should see about 13.5v and your should see about 14v at 2500rpm. The 2500rpm reading should not drop much if you load the system by turning on the headlights and the HVAC blower to high. If you don’t see those voltages the alternator isn’t working correctly.

      In many cases the cause will be worn brushes in the regulator/brush assembly. But that isn't necessarily a conclusive test as the alternator bearings won't be under load. If the alternator bearings are in good condition a new regulator/brush assembly may be all that is needed.

      If you remove the alternator belt, you can check the condition of the bearings. f the bearings are really bad, that will be apparent. The regulator can be replaced without removing the alternator from the car. When removing the belt you must loosen the pivot bolt at the bottom of the alternator. The top adjustment/lock is obvious, but if you don’t loosen the pivot bolt you’ll damage the adjuster (it it already hasn’t been damaged). If the adjuster is inop, a pry bar can be used to set belt tension.

      On an E30 another possible problem that will prevent the alternator from working is the battery warning light in the cluster. If that bulb is burned out (doesn’t come on when the ignition is switched on) it won’t supply exciter power to the alternator and thus the alternator won’t charge. At some point in the production run a resistor was added in parallel to the bulb to avoid a burned out bulb from preventing the alternator from working. But I don’t know when that happened.

      If you have to replace the alternator, do not get a generic reman (cheap) unit. Those have been known to not work out-of-the box or fail shortly after installation. Use only a genuine factory rebuilt unit. It will cost more, but it will work out of the box and likely work for a long time.

      As an FYI some info on batteries is:

      %chg Voltage S/G
      100 12.7 1.265
      75 12.4 1.225
      50 12.2 1.190
      25 12.0 1.155
      0 11.9 1.120

      Sulfation of batteries starts when specific gravity falls below 1.225 or voltage measures less than 12.4. Sulfation hardens the battery plates reducing and eventually destroys the ability of the battery to take and hold a charge.

      Only 30% of batteries sold today reach the 48-month mark. In fact 80% of all battery failure is related to sulfation build-up. This build up occurs when the sulfur molecules in the electrolyte (battery acid)become so deeply discharged that they begin to coat the battery's lead plates. Before long the plates become so coated that the battery dies.

      In the general case you can figure on 6 years as being the useful life of a battery, even if it has never suffered from deep discharges.
      Last edited by jlevie; 08-30-2015, 09:15 AM.
      The car makes it possible, but the driver makes it happen.
      Jim Levie, Huntsville, AL


        Brake and Clutch Hydraulics

        Assuming that the brake and clutch have been properly bled, when experiencing problems with the brake system (or clutch on a manual) the first check is to look for leaks at the the calipers, slave cylinder, and lines. If there are no leaks in the brake system, and especially if you experience a sinking pedal, the master cylinder is bad. The brake master cylinder can (and usually does) leak fluid into the brake booster. Check for that with a rag on the end of a wire and see if there is fluid in the bottom of the booster.

        If you find fluid in the booster, it must be replaced as brake fluid will destroy the diaphragm in the booster in short order (ask me how I know). It doesn’t matter whether you have an ATE or Girling master cylinder and booster, but both need to be from the same manufacturer. It is best to bench bleed the master cylinder before installation. Whenever I have to replace a master cylinder I’ll also replace the reservoir and seals.

        In a like manner if there are no leaks in the clutch slave, or soft line, the clutch master cylinder is bad. Usually the leak will be internal and there will be no evidence as to what is wrong. Meaning that the clutch master needs to be replaced. In the general case, the clutch master, slave, and soft line will be of the same age. So if I have to replace one part I’ll replace everything. Do it once and do it right.

        Brake calipers are pretty easy to rebuild with inexpensive kits (I get OEM parts from or you can get rebuilt calipers. If the car has ATE calipers, replace the guide bushings and perhaps the guide pins (if corroded) when rebuilding the calipers. A little soap solution makes it easier to install the guide bushings, but otherwise no lube is needed. However, you do need to lube the seals with brake fluid.

        A little compressed air will pop the caliper pistons out. Wrap the caliper in a rag to avoid making a mess. With a caliper off, the brake system will gravity drain through the open line. I have four fittings salvaged from a wrecked car that I use to plug the lines. But a double thickness of plastic storage bag secured with rubber bands will work.

        In the rear there are four soft lines. The ones that connect to the calipers are pretty easy to replace, but the ones that go to the tee junction above the rear subframe can be a pain. High quality flare wrenches (read SnapOn or Mactools) reduce the likelihood of stripping the flare nuts. Also, liberal application of PBlaster or Kroil several days before working on the system can help. And a bit of heat from a flame wrench (MAPP or oxyacetylene) can also help.

        Top quality SS lines, like from Bimmerworld or Turner, are okay but not needed. I have seen lesser quality SS lines separate at the fitting on several occasions, but I’ve never seen an OE line fail if it was in good condition (no cracks and not ancient). I’ve used both and can’t tell any difference in brake feel. Quality SS lines are more expensive, so I only use OE/OEM soft lines now.

        Working room above the subframe is extremely limited. I usually just lower the subframe a couple of inches to get room to work. At most you will have to lower the rear of the exhaust (and support it).

        Don’t cheap out on brake/clutch parts. Get OE or OEM parts. The generic stuff has been known to fail to work out of the box or fail shortly after installation. The OE/OEM parts lasted 30+ years and you can expect them to work out of the box and continue to work for another 30 years.
        The car makes it possible, but the driver makes it happen.
        Jim Levie, Huntsville, AL


          Brake System Flush & Bleed

          Usually it is best do a flush and bleed at the same time as the fluid is to be changed every two years.

          A pressure bleeder, which isn’t expensive, makes this an easy one person job. One liter of ATE Type 200 fluid is more than enough for a full flush/bleed on a car with a three channel ABS. You will need about 1.5 liters on later cars with the four channel ABS system.

          The ATE fluid has proved to be resistant to moisture absorption, by testing. Which means that there is little chance of rusting or boiling of the fluid under hard braking conditions. It also has a reasonable boiling point, high enough to make it suitable for track/race use in a stock E30. Those cars with a lot more power that see the track should use Castrol SRF and change it once a year or sooner.

          Start by sucking the old fluid out of the reservoir (a turkey baster or large syringe works). Then connect the filled bleeder and pump it up to about 15psi.

          On early cars with the three channel ABS system like an E30, push a measured 200cc of fluid through each rear caliper and a measured 150cc through each front caliper. Push a measured 100cc through the clutch system on a manual transmission car.

          On later cars with the four channel ABS system, push a measured 350cc of fluid through each rear caliper and a measured 150cc through each front caliper. Push a measured 100cc through the clutch system on a manual transmission car.

          It doesn’t matter which rear wheel you start with, but the last caliper should be the left front. When the flush/bleed is finished, turn the bleeder upside down and drain fluid from the bleeder to fill the line on the reservoir and clear the hose of fluid. Then when you remove the cap from the reservoir you won’t have fluid spraying out and making a mess.

          Toss any left over fluid to avoid taking a chance on it absorbing moisture. If the brake & clutch system has no leaks you will never have to top up the system and thus have no use for the left over fluid.

          If you do spill brake fluid, wipe it up and then clean with water, or better yet spray the are with something like Simple Green and was that off with water. Brake fluid will eat up paint.

          A failure to bleed a caliper could be a plugged bleed nipple, a collapsed soft line, a pinched hard line, a bad master cylinder, or a stuck valve in the ABS unit. Cracking the line at the ABS (input and output) unit will tell where to look next. In a like manner cracking the soft line where it mates to the body lines and the caliper will narrow the search area.

          The brake master cylinder has a section for the front brakes and a section for the rear brakes. So it becomes a suspect if neither rear caliper will bleed or neither front caliper will bleed.
          Last edited by jlevie; 08-30-2015, 08:51 AM.
          The car makes it possible, but the driver makes it happen.
          Jim Levie, Huntsville, AL


            Check Panel Brake Warning Light

            The most common problems that result in the Check Panel brake warning light being on after pressing the brake pedal with the engine running (or the light coming on while driving) will be a bad brake light switch, the wrong or aged bulbs, or corrosion in the bulb sockets.

            So when faced with this problem the first action is to make sure that you have the right bulbs with the plated bases. I get mine from my dealer to be sure I have the right ones. If the glass envelope of the bulb shows any darkening, replace it. The filament will have lost material, be of higher resistance, and trigger the warning. Be careful cleaning the sockets. A brass bristle brush is the only safe way of removing oxidation without harming the plating of the socket. If the bulbs are okay, you may need a new (OE or OEM) brake light switch.

            The way the system works is that there is a reed switch wrapped in the wire that powers the bulb. If sufficient current flows through the wire when the brake pedal is pressed the reed switch will close. All three of the brake lights have one of these reed switches and since they are wired in series all must close for the Check Panel to believe that all of the brake lights are working. That can make diagnosing this problem difficult as there is no easy way to identify which reed switch isn’t closing.

            The switches for the rear brake lights are in a module mounted in the left rear fender well, but the switch for the third brake light is a part of the light fixture.

            Bad harness contacts or wiring faults are also possibilities. And the Check Panel itself could be bad.

            In a worst case situation I’ve had to identify the brake light wire, cut it and measure current flow, and then splice it back together in order to ID the offending circuit. Then I have to figure out why the current flow is lower than normal.
            The car makes it possible, but the driver makes it happen.
            Jim Levie, Huntsville, AL


              Cooling System Bleed Procedure

              1) Using ramps or a jack get the front of the car 1' or more higher than the rear. That will make the radiator and bleed screw the highest point on the engine and facilitate removal of air.

              2) With the bleed screw open, add coolant until no more air comes out of the bleed.

              3) Leave the filler cap off, or at least loose, and set the heat for max temp and fan speed. Leaving the cap loose will prevent air that's still in the system from causing a "coolant fountain" once the engine heats up. Start the engine and allow it to warm up to operating temp. As it warms up occasionally crack the bleed screw to release any air and top up the coolant as necessary.

              4) Once the engine is at temp bring it up to 2000-2500rpm for a few seconds several times. Then crack the bleed until no more air is released. At this point the heater should be throwing lots of hot air, which indicates that the heater core is filled with coolant. You may have to repeat this a few times to get all the air out.

              5) Drive the car a bit, allow it to cool back down, and recheck the bleed for air. Over the next few days you may get very small amounts (a few bubbles) of air out of the bleed screw.

              A vacuum fill bleed system makes filling and bleeding the cooling system a trivial task. But the procedure above will work if you don’t have access to a vacuum fill system. On an E30 and some other BMW’s you can speed up the fill process by removing the small hose that runs from the coolant reservoir to the top of the radiator at the radiator end. Then fill the reservoir to the mark, screw on the cap and blow into the hose until coolant comes out of the radiator nipple. That will fill the engine and radiator with coolant pretty quickly. It may take more than one fill/blow cycle to fill the radiator. Then bleed as per above to get any remaining air out.
              The car makes it possible, but the driver makes it happen.
              Jim Levie, Huntsville, AL


                Cooling System Flush Procedure

                If the cooling system has been properly maintained (coolant change every two years) and the coolant doesn’t look dirty, a flush is probably not necessary, A simple drain, refill, and bleed is all that is needed. Otherwise you might want to flush the cooling system. The older the car the greater the odds are that a flush will help.

                1) Get the front of the car 1-2' in the air on jack-stands.

                2) Drain the coolant at the radiator and block, if possible remove the thermostat so you will have full flow through the cooling system even if the engine is not at normal operating temperature, and set the heater controls for full hot. You can't do this on a later engine with the MAP controlled thermostat. O-ring sealed thermostats require you to make up a temporary gasket, which can be made out of pasteboard.

                3) Add flush compound and fill with plain water. Then run the engine at normal temperature as specified by the flush manufacturer (usually about 15 minutes at operating temperature). In cooler weather it may be necessary to block off some of the air into the radiator to decrease the warmup time.

                4) Allow the engine to cool until you can place your hand on the cylinder head with out discomfort. Drain the system and refill with plain water.

                5) Run the engine for 10-15 minutes or until temp is close to normal.

                6) Repeat (4) and (5) until the water drained from the system is clear and free of debris.

                7) Fill with coolant. Use BMW Blue coolant mixed 50:50 with distilled water. Tap water contains dissolved oxygen and may contain minerals. Either of which will reduce the lifetime of the coolant.

                8) Then bleed the system


                You don't absolutely need to remove the thermostat, but doing so will allow continuous flow through the radiator and will also make draining & filling faster and easier.

                Always allow the engine to cool to the point that you can hold your hand on the cylinder head without discomfort. That will prevent scalds from hot coolant and prevent thermally shocking the head when you dump the coolant.

                Filling the system with hot water makes the process go faster and keeps from having to run the engine a lot in a cold condition (rich mixture).

                A few ounces of Cascade dishwashing detergent is a reasonable substitute for a commercial flush compound.

                A rusty cooling system needs an oxalic acid flush. Kits for that (containing oxalic acid and soda for neutralizing the acid) used to be available, but aren’t now. Citric acid also works, but not as well on rust as oxalic acid. 6oz of oxalic acid and 4oz of soda will treat a 1-1/2 to 2-1/2 gallon cooling system. The procedure is like the above with an extra step 4 where the soda is added before the series of fill/drains are done. An engine that needs this treatment probably has a pretty severely clogged/damaged radiator and heater core, which strongly suggests that they be replaced after using this procedure on the cooling system. A cooling system that needs this treatment should have a detergent flush, the acid flush, then another detergent flush. The initial detergent flush will clean out any oil, which would interfere with the acid flush, and the final detergent flush helps to wash out loosened sediment.

                Note that the cooling system should be replaced about every 100k. There are plastic and rubber parts in the cooling system that degrade with time and can suddenly fail. As can the water pump bearings & seal. If that happens on the highway and you don’t see the rise of the temp gauge in time serious engine damage can occur. Better to replace the system on schedule than to risk a failure. Replacing the cooling system means a new radiator, fan clutch, water pump, thermostat, reservoir, cap, and all hoses. If damaged or cracked, replace the fan.

                The proper coolant is the BMW Blue coolant mixed 50:50 with distilled water. The dissolved oxygen and possible minerals in tap water will degrade the corrosion protection package in the coolant and shorten it’s life.
                Last edited by jlevie; 08-30-2015, 12:20 PM.
                The car makes it possible, but the driver makes it happen.
                Jim Levie, Huntsville, AL


                  Parking Brake Adjustment

                  The correct way to adjust the parking brakes is:

                  1) Lower the hand brake and loosen the cable adjusters.

                  2) Working through a lug bolt hole turn the star adjuster with a flat-bladed screwdriver until the wheel locks. I just turn the adjuster until it doesn't want to turn any more. Then back off the adjuster 12 clicks. The book says 8 clicks, but I’ve had the shoes drag at that setting, so I use 12 clicks. Repeat for the other wheel. Note that the star adjuster is at the 6 o'clock position on later cars, but at the 10-11 o'clock position on an E30.

                  3) Raise and lower the hand brake several times to settle the cables. Then raise the lever two or three clicks and tighten the adjusters until the wheel can just be turned with moderate force.

                  If you have never had the rear rotors off, it would be a good idea to back the star adjusters all the way off and pull the rear rotors to see if the parking brake shoes are badly worn or if there are other problems in the parking brake mechanism.

                  In salt rich environments it isn’t unusual to find that the backing plates have rusted out where the compression pin locks into the backing plate and the shoes aren’t being held against the backing plate. The parts to fix this aren’t expensive, but the bearing hubs have to be removed to change the plates (which means new bearings). The fronts are pretty easy, but the rear hubs are a pain if you don’t have access to a Sir Tools B90 kit.
                  The car makes it possible, but the driver makes it happen.
                  Jim Levie, Huntsville, AL


                    E30 Lubricants

                    Our E30’s have sliding rocker arms and were designed in the days when oils with high levels of ZDDP (a lubricant for sliding surfaces) were common. Most all current oils have low ZDDP content. One story is that the ZDDP is bad for catalytic converters, though cars of that era had converters and there wasn’t a high failure rate that could be directly attributed to the ZDDP levels. Another story is that modern engines don’t have the sliding surfaces and don’t need ZDDP and ZDDP in the oil is a bit of a problem for oil recyclers. I tend to believe the latter.

                    To limit rocker wear you want an oil with high levels of ZDDP. One “street” oil that satisfies this requirement is Amsoil Z-Rod 20w50, another is Shell Rotella T, though I have seen some data that suggests that Shell has lowered the ZDDP content slightly. While there are several racing oils that have higher ZDDP content, they don’t have the detergent packages as they are meant to be changed frequently, like after every event or two. Consequently they aren’t a good choice for a street car.

                    I live in the south and use 20W50 year round. In cold weather (temperatures from 60 to -20F) 10W40 would be better.

                    According to what I have been able to find out ( a Mobile-1 filter seems to be the best choice with the BMW OE or Mann filter running a close second. I have seen cheap generic filters collapse and block/limit oil flow (not a good thing).

                    These engines run dirtier than modern engines and have more combustion byproducts blow by than more modern engines. That builds up in the oil and can cause gunk to form, depending on the car’s typical driving cycle. An urban cycle (lots of short low speed trips) won’t get all of the engine up to the temperatures needed to boil off the condensates and gunk will form. But a primarily rural cycle with frequent weekly trips of 20 minutes in moderate weather or 30 minutes in colder weather will get all of the engine hot enough to boil off the condensates. The nicest thing you can do for an E30 that sees a mostly urban cycle is to take it out for a 30 minute run at highway speeds once or twice a week and shorten the oil/filter change interval.

                    Because of the condensates you can’t take advantage of the longer life of synthetic oil. How often to change the oil and filter is determined by your driving cycle. A purely urban cycle suggests an oil/filter change every 2500-3000 miles. A rural cycle can go to the SI service interval lights.

                    I like Redline 75W90 (which contains friction modifiers) for limited slip differentials and Redline MTL 75W90 in the transmission. But a high quality ATF like Redline D4 in the transmission also works very well, especially in colder weather..

                    As far as I can determine from looking at the part numbers in the BMW ETM, the internals of a G260 transmission were essentially unchanged over the production life, even though the transmissions may have a colored tag indicating what fluid to use. A factory BMW tech rep told me that the color tag was meant to indicate to a BMW tech what fluid to use to top off a transmission. He had no idea why BMW used different fluids at different points in the production run other than changes in suppliers. If you are draining the fluid and filling with fresh you can, in my opinion, ignore the tag.
                    Last edited by jlevie; 08-31-2015, 09:18 AM.
                    The car makes it possible, but the driver makes it happen.
                    Jim Levie, Huntsville, AL


                      Engine Cleaning

                      When faced with a dirty engine and/or engine bay the process I use is:

                      1) Start with a hot engine and get front of the car up on jack stands. Several large pieces of cardboard under the engine area will soak up the grunge and help prevent stains.

                      2) Using a putty knife, screw driver, etc., scrape off any heavy deposits. Most of that will be on the lower part of the engine and you'll have to get to it from underneath.

                      3) Spray a mixture of Gunk and diesel or kerosene on using a small garden sprayer.

                      4) Scrub every thing you can reach using plastic bristle brushes on painted surfaces and wire brushes on bare metal. Work heavily caked areas again with the scrapers. Spray on more solvent mixture as needed.

                      5) Re-fill the sprayer with any concentrated detergent (Simple Green, pressure washer detergent, etc) and spray everything down.

                      6) Using a garden hose set for a gentle spray, or better yet a plant watering wand, wash down the engine and engine bay. You want to avoid any high pressure spray as that may force water into places that you don't want it to go.

                      7) Spray on more detergent and go over everything with the brushes, then repeat (6).

                      8) Leave the hood open and allow the engine bay to dry for at least 8 hours before starting the engine.

                      Notes: Having the engine hot will make oil and grease easier to wash off and the residual heat will help dry out any water that reaches electrical parts. You won't get the cosmoline/oil stains off the valve cover on an m20/30 engine as they are baked on. The best way to clean up the valve cover is to have it bead blasted or hot tanked, but you can get most of it off with paint remover (with the cover off the engine).
                      The car makes it possible, but the driver makes it happen.
                      Jim Levie, Huntsville, AL


                        Engine Management Diagnostics

                        Idle, hard starting, and engine operation problems are most commonly caused by intake leaks and/or a sticky or defective Idle Control Valve (ICV). The only reliable method of locating intake leaks is to have a smoke test run on the intake and crank case and to test the brake booster with a gage and vacuum pump. The complete list of possible causes of an intake leak is:

                        Intake boot
                        Throttle body gasket
                        ICV hoses & connections
                        Brake booster, hoses, and connections
                        Crank case breather hose
                        Evaporative control hoses, valve, and expansion tank
                        Fuel pressure regulator & hose
                        Injector seals
                        Valve cover gaskets & bungs
                        Oil filler cap
                        Dip stick o-rings
                        Oil return tube o-rings
                        Pan gasket or oil level sensor gasket

                        While leaks in some of those can be found by inspection or by spraying carb cleaner on suspect areas, not finding leaks that way doesn't eliminate the possibility. Only a properly executed smoke test using the right equipment will really work. That means plugging the exhaust, replacing the AFM with a plug containing a nipple for smoke injection, and using a professional smoke machine that uses oil for long persistence smoke. Then you pressurize the intake for about 10 minutes at 2-4psi with long persistence oil smoke and watch for smoke. Note that if there is a major leak, it must be repaired and the test repeated.

                        Once the possibility of intake leaks is eliminated, the ICV needs to be removed and cleaned with carb cleaner until the vane inside moves freely. When the ignition is switched on you should be able to feel vibration from the ICV. If no vibration the ICV is bad, there's a problem with its wiring or connector, there's a problem with the TPS, or the DME (or Idle Control Module (ICM) on an ETA car). Early M20B25 cars with the 153 DME are known for unstable idle problems. Replacing the 153 DME with a 173 or later fixes that and also also allows the stomp test to work.

                        For the DME (or ICM) to control idle, the idle switch in the TPS must work correctly. The switch should close when the throttle stop is 1mm off the idle stop screw. Hearing a click doesn't mean the TPS is working. Check with a meter or test light by removing the back shell on connector and checking for the signals at the DME (or ICM) with the ignition on.
                        Oil can, and will, get into the TPS. The switches are simple exposed metal parts and oil will interfere with the operation of the TPS. I always drill a 1/8-3/16 hole in the center of the round boss on the bottom of the TPS to provide a path for the oil to escape.

                        On an ETA car the cold start valve and it’s associated sensors must be functional.

                        The fuel system should be tested via the suite of tests in the Bentley manual as invalid rail pressure can be a contributor to idle and starting problems. A simple injector check is to pull the injectors, jumper the fuel relay to run the pump, and see if the injectors are leaking. You can also point the injectors into a towel, remove the coil wire, and crank the engine to see if all of the injectors appear to be spraying in a similar fashion. The best approach to possible injector problems is to have the injectors cleaned and flow tested. Since raw fuel can or will be released in these tests, have a fire extinguisher handy. I use RC Engineering for cleaning, rebuilding, and flow testing. I will always do the injectors on an an engine with 100k or more one it. A noid light will prove that each injector is seeing a firing signal.

                        While a bad check valve in the high pressure pump can result in longer than normal cranking, if the fuel system is working as it is supposed to the rail will reach normal pressure in a few turns of the engine. A weak pump, clogged filter or leaking FPR in conjunction with a failed check valve can result in longer cranking and/or idle problems.

                        The O2 sensor can be a contributor to idle and performance problems. The O2 sensor is a scheduled maintenance item with a useful life of no more than 60k. If the sensor has that mileage or more (or is of unknown age), replace it. A good O2 sensor is vital for proper operation of the engine. The DME uses that data to adjust fuel trim for stoic operation. An aged sensor typically indicates a leaner mixture than actually exists, which results in the engine running richer than it should.

                        The ignition system can be contributor. Unless recently replaced with OE or OEM parts, install a new distributor cap, rotor, and wires. Use only OE or OEM parts. The third party (cheaper) stuff is an iffy proposition. Use NGK ZGR5A plugs as they are the closest to the original plugs that are NLA. If in doubt, replace the ignition coil with a new OE or OEM part.

                        The AFM can be a contributor. If the vane doesn't move freely or the resistance track is worn the DME may be receiving invalid data from the AFM. And if someone has fiddled with the bypass air adjustment the DME may be unable to stabilize idle. The bypass air adjustment should only be adjusted per the procedure in the Bentley and with an exhaust gas analyzer. And even then everything else associated with engine management has to first be operating properly. If the AFM becomes a suspect, replacement with a good used unit is the best approach.

                        Improperly adjusted or malfunctioning valves will affect idle, starting, and operation. As can compression issues from ring or cylinder wear or from the valves. A valve adjustment is called for every 15k. A useful diagnostic is to run compression (dry and wet)and leak down tests on the engine. Those tests will tell if the rings and valves are in good condition and the leak down test will usually indicate whether it is a cylinder or valve problem.

                        Although not usually a problem, a bad DME temp sensor is a possibility. That generally won't cause an unstable idle, but can cause hard cold or hard hot starts and/or a rough idle. As can problems with the timing reference sensors. Although not commonly encountered, a bad harmonic balancer on an M20B25 or M30 engine will cause problems.

                        When all other possibilities have been eliminated and idle, starting, or operation problems persist, replacement of the DME, or if applicable the ICM, is indicated.

                        In many cases the cause of problems will be a combination of factors. So it is important to test and repair all of the possible causes.
                        Last edited by jlevie; 09-13-2015, 04:19 PM.
                        The car makes it possible, but the driver makes it happen.
                        Jim Levie, Huntsville, AL


                          Excessive Parasitic Draw

                          Normal parasitic draw on an E30 (and most other BMW’s) is 30-40ma. That is measured by disconnecting the battery ground cable and placing a DMM in current mode between the battery negative post and the ground cable. All doors and the trunk must be closed for this test.

                          If you see more current draw, pull one fuse at a time to try to find the offending circuit. Then use the factory wiring diagrams at to trouble shoot that circuit. There are a few things in the car that are powered all the time (OBC, cluster, alternator, DME, and door lock module). Of those only the alternator and DME are not fused, as I recall. So if you can’t find the cause by pulling fuses, try disconnecting the alternator (it may have a bad regulator), the cluster, door lock module or the DME.

                          The most popular cause of excessive draw is improperly installed aftermarket electronics and the test for that is disconnect said equipment.
                          The car makes it possible, but the driver makes it happen.
                          Jim Levie, Huntsville, AL


                            Head Gasket Leak Diagnostic

                            Obviously if you have coolant in the oil or oil in the coolant the head gasket has failed and the head is probably warped. But another case is a simple loss of coolant.

                            A pressure test of the cooling system will tell if there are leaks and where they are. If the test is negative on a cold engine, repeat the test on a hot engine. Occasionally one will encounter a water pump that sporadically leaks while the car is being driven, but that will leave coolant residue on the front of the engine. When running the pressure check be sure to look under the car for fluid draining from the heater core

                            If testing and observation can't find leaks, the loss of coolant will be from a head gasket leak that is pumping air into the cooling system. At some point the pressure will get high enough for the cap to lift to release the pressure, which will dump some coolant. That may only happen while the car is being driven and leave no evidence as to what happened.

                            The definitive test is to pressurize each cylinder for several minutes with 170-180psi while monitoring cooling system pressure with a 0-5psi gauge. A negative result on a cold engine requires the test to be repeated on a hot engine. But I have seen a couple of cases where this test didn’t work, but what follows did.

                            A DIY test for a leaking head gasket is to remove the cap to vent any pressure when the engine is completely cold (like after sitting overnight). With the cap back on the hoses will be soft. Drive the car for a bit and let it completely cool down again. If the hoses are hard then, air is being pumped into the cooling system. An alternative test is to fully bleed the system, drive the car, and re-bleed. Release of a significant amount of air on a re-bleed is evidence of a head gasket leak.
                            Last edited by jlevie; 08-30-2015, 01:17 PM.
                            The car makes it possible, but the driver makes it happen.
                            Jim Levie, Huntsville, AL


                              Intermediate Shaft Bearings

                              The bearing part numbers are:

                              Measure the IM shaft diameter after polishing, chuck the bearings up in a lathe, slow speed, and bore to initial size. Use a standard cam bearing installation tool and install them in the block, they will crush and become smaller than the diameter of the shaft. Hand finish with a brake cylinder hone, low speed, a little goes a long ways. Test fit and measure with a bore gauge and finish sizing with green scotchbrite. Oh yeah, make sure the front bearing lines up with the oil feed hole from the #1 main bearing feed (The second bearing does not matter as it is fed through the shaft from the front journal)

                              You want about .001-.0015" clearance, I would say .002" max Anything more then that and you risk loosing too much oil pressure.

                              Normal wear is the usual cause for replacing the intermediate shaft bearings. But if the block is hot tanked the bearings will be destroyed.
                              Last edited by jlevie; 08-24-2015, 02:57 PM.
                              The car makes it possible, but the driver makes it happen.
                              Jim Levie, Huntsville, AL