ICV - nothing happens when I unplug it!

[jlevie]

Okay, it sounds like you have eliminated the obvious suspects. Check to see if the idle switch signal is reaching the DME. If it is I'd try a different DME. It may not be sensing the idle switch.

You could also try adjusting the throttle stop and TPS. To do that, get the engine to operating temperature and disconnect the ICV. Adjust the throttle stop for an idle of 950rpm. Then check to see that the idle switch closes when the throttle arm is 1mm off the stop screw. When you reconnect the ICV the idle should stabilize at 750rpm.

[monkeyodeath]

I'll try adjusting the throttle stop again.

I'm pretty sure that the DME is sensing the TPS. When I disconnect the TPS, there is a pronounced change in engine speed - it actually goes back up to about 750.

When I use a wire to bridge the TPS connector to simulate idle switch position, the idle settles back down to 550-600.

[monkeyodeath]

Okay, really broke into this thing last night. Tested the connections for everything at the DME, really cleaned out my ICV, checked the air temp sensor, rechecked the coolant temp sensor at both DME and the sensor itself.

I managed to get the idle slightly higher than it was. I'm beginning to wonder if my tach isn't off a bit, because the idle is very sticky to that exact point. Very hard to get it to change.

I tried a couple of experiments.

First, I disconnected the ICV and applied 12v to the center terminal and grounded one of the outside ones. The ICV snapped open and my idle surged, bouncing up and down pretty high. Reconnecting the ICV connector brought it back down to where it was. I think that the ICV is not gummed up.

I disconnected the ECT sensor and bridged the harness connector with a 1M resistor. Idle went up to about 750-800.

I tried a replacement DME. At first, the idle is at 750 rpm upon starting, then settles down after 30 seconds or so to 600 ish.

I also tried resetting the idle as per jlevie's instructions, but here's the weird thing:

With the ICV disconnected, turning the screw to open the throttle plate had very little effect, until I opened the throttle plate enough that it tripped the idle switch on the TPS. Then the idle jumped up to 750-800. Was really hard to get it to stabilize at 950, because, even with the ICV disconnected, the idle would jump when the TPS was switched out of idle.

I'm still noticing that, on startup, if I immediately start driving the car, or blip the throttle, the revs jump, then drop to 300 rpm or so, then bounce a little bit before stabilizing. This happens for the first 30 seconds the car is on, then after that it's fine.

Finally, how cold of a day does it have to be for the engine to hold high revs for a cold start? And how long does it keep those high revs before it drops back down to normal? I'm used to cars that spend a good minute or two revving higher on a cold start before dropping back to normal.

Is my tach just way off?

[jlevie]

What DME do you have?

[monkeyodeath]

what dme do you have?

173

[jlevie]

Now that is weird. With the ICV disconnected the DME has no way to change idle speed so it should not matter whether the idle switch of the TPS is closed or open. The speed should be a direct function of how much air passing through the AFM.

How old is the O2 sensor? If it is of unknown age or has 100k on it, replace it.

[monkeyodeath]

O2 sensor was replaced 1.5 years and at most 5k miles ago.

[TimWis]

Hmm.... im having the same problem... im ruling out the O2 sensor or TPS.... the service engine light comes on at a stedy idle and goes away when i leave a stop and go intersection...

[TimWis]

didnt mean to ninja your thread either lol

[monkeyodeath]

no worries. this is so weird. how is the DME changing the idle speed? timing? fuel mix?

[nando]

It also uses timing to adjust idle but primarily it's set by the icv.

[monkeyodeath]

haha, anyone have anymore ideas about this? or do we just file under "weird and unexplainable"?

[dr.strangelove]

Bumping this back up! I have been having very similar issues since i've owned this ix of mine.

Any more information on this would be great, jlevie, looking at you here for some updates.

[jlevie]

Without more information about the car, start with:


Idle or hard starting 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

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 smoke test will really work.

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) is faulty.

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 0.030-0.060" off
the idle stop screw.

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.

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.

The O2 sensor can be a contributor to idle problems. The O2 sensor is a
scheduled maintenance item with a useful life of no more than 100k. If the
sensor has that mileage or more (or is of unknown age), replace it.

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 and starting. As
can compression issues from ring or cylinder wear. 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. Aged ignition wires, plugs, distributor
cap, or rotor can cause problems. Insulation does break down with time and
heat. And since the youngest E30 is going on 20 years old, if the ignition
system is original or the plugs are old replacement is indicated.

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 or starting
problems persist, replacement of the DME, or if applicable the ICM, is
indicated.

[amcink]

Did you test\check the ICV computer (relay) green in color under the glove box?