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Multiple Problems

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    Multiple Problems

    I need some advice and insight as to what the solutions are to a couple of problems I have with my '91 Vert. as I can't find much on them too specifically, so I though I'd make a post so you guys can help me out. Again, I'm not totally sure if this is where this belongs or if this issue has been covered in another thread. So, my apologies if I'm wrong.

    Just recently I have done the whole: "Mess Under the Intake" deal with all new vacuum and fuel hose where needed, as well as new gaskets, rebuilt 318is injectors O-Rings, clips, etc.
    I also capped off both coolant nipples on the engine, and has been working fine for me so far. And so viewers are aware, these are all problems that have been accumulating over the past month, the most recent being the fuel issue.

    Anyways my main problem is that just recently while I was driving the engine began to struggle to accelerate and began to pop and bang. (No muffler right now) The way it would accelerate was if I was flat out on the throttle. My thought is that it could be that for whatever reason the injectors are injecting too much fuel, causing it to bog when normally driving, popping when letting off the throttle, and running smoother when at full throttle. I'm not sure what could cause this other than possibly an electrical problem. Just about everything else fuel-wise is fine, I replaced the fuel filter and pump a few months ago.

    Another problem of mine is that the idle is very rough, I have adjusted the idle screw so it idles at around 1k but it fluctuates from time to time. My thought is that it's the Idle control valve, I cleaned it out but it might just be too old and need to be replaced.

    Next are vacuum leaks. Like I said, nearly everything on the intake side of the engine was replaced. But it still sounds like there's a leak somewhere and I can't seem to find it, any leads on where that could be would be hugely appreciated.

    And fourth is somewhat hard to explain. When I floor it, it has less power than if i were to release it a bit. It feels almost if the throttle cable it being overextended or maybe its too short? I honestly am not sure, but it seems as if after a certain amount of throttle is applied it slacks up. Causing it to not be as open as it could be. Maybe this just needs to be adjusted.

    So, my main questions are:

    1. What could be causing the alleged too much fuel problem?

    2. What can I do to fix the idle?

    3. Is there any other areas I should look or specifics on vacuum leaks?

    4. Would a loose or worn throttle cable be the cause of less throttle when pushed all the way to the floor?

    Any help or tips is appreciated.


    Running rough often seems to be the engine not knowing where TDC happens to be, so I'd start with testing the cam and crank sensors, then move on to the TPS and coolant sensor. You could also start by unplugging one electrical device at a time until the symptoms remain the same. If everything is in spec you may have the crank trigger wheel separation that we are all having these days, in fact, just last week the second one on my car separated.

    Your throttle cable shouldn't be an issue as long as the plate is seated, generally, if seated it should pull the plates to full with no issues, but it's always nice to confirm if you can.

    Any codes to share?


      "Injecting too much fuel" is extremely rare for these engines, being that the fuel is 100% managed by the ECU. The only culprits that I can think of are the coolant temp sensor (this one has a big effect on fuel injection), and a failing crank position wheel (ECU loses sync and does not fire the ignition, allowing raw fuel into exhaust). I had my crank positoin wheel go out on me and it caused many of the symptoms that you describe, mainly the poor idle.

      As always, do a thorough check for vacuum leaks.

      The throttle cable does not stretch. If you can verify that it operates as expected by pushing the pedal while looking at the throttle body (hood open), then it is fine. This could be a sign of a dying AFM. Those do tend to read low (or not at all) when the resistor track wears out.
      Last edited by bmwman91; 08-20-2019, 11:48 PM.


        Thanks for the insight. As for codes I don't have a reader or anything for the car if that's what you mean. If it means anything a green dash light with two arrows comes on when it tries to run, as it cant hold an idle.
        Otherwise the coolant temp sensor might be one of many issues because as I stated I had done the whole mess under the intake as well as flushing and refilling the coolant. Although the temp gauge on the dash reads to the left dash.
        And I was worried it would be the AFM as well, as I believe those are very expensive new/rebuilt and are difficult to rebuild yourself. A lot of what I've seen about rebuilding these is that it is very difficult and isn't worth doing. My only concern is that I'd rather not buy a used one to have this problem again in the next however many miles it lasts. I'm definitely not opposed to rebuilding it, because it's going out then why not try? But maybe I am not fully understanding if it can be fully rebuilt at home as I've never taken one apart before.

        Thanks again for your help. My only questions are how difficult is it to replace all of the sensors and the position wheel and how exactly big of a job is the crank trigger wheel? My thought is that I'll take care of that and anything else while it's torn apart.
        If there's anything you can think that I should do while I have it apart that'd also be some good information so I can snag all the parts online and knock it out in a weekend. (Hopefully)
        Last edited by e30_jake; 08-20-2019, 06:10 PM.


          Well, you should test parts before you replace them, but if you want to throw money at it: cam and crank sensors, new injectors, throttle position sensor, management coolant sensor, ICV, and let Bav Rest rebuild your AFM.

          Codes can be read via the "stomp test," which is keying the car to on but not start, and depressing the throttle pedal fully within 5 seconds. Codes will then flash via thw CEL.

          If find codes please report back after reading up, and test resistance on the sensors mentioned above as per spec.


            The AFM is pretty easy to deal with. Pop the top off, hit the track with some contact cleaner, and if it is so badly worn as to mess with the output, try adjusting the wiper so that it makes contact at a slightly different radius on fresh carbon track.

            The coolant temp sensor for the ECU is different from the sender for the instrument cluster. It is fairly cheap, and while they rarely go out, it might be worth doing. Also check the wires at the connector plug for it as I have heard of those fatiguing and breaking to cause intermittent issues.

            The crank trigger wheel is super easy to replace, but it is also $$$. They are also likely to be out of production at some point in the not too distant future. I got one earlier this year for $500, and it took like 3 weeks because all of the remaining ones seem to be in BMW warehouses in Germany. You can check yours by removing it, cleaning it, and inspecting for cracks in the rubber. Basically, you should not be able to cause ANY axial play between the outer ring and the inner hub when pushing by hand. If you can, then the rubber is failing, and it will only be a matter of time before it goes entirely. See here:
            (note: you do not need to remove the big crank hub bolt to get the damper wheel off)


              Have you run a compression test to make sure the basic mechanical s are sound?