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Re: Rough idling 88 E30 M3 (archive)

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Posted by Angus on May 02, 2000 at 13:53:17:

In Reply to: Rough idling 88 E30 M3 posted by WJCarnes on May 02, 2000 at 12:54:51:

: I have an 88 M3 with 138k on the odo. The car is probably completely stock. I have modified nothing.
: Intake gaskets were resealed and then replaced. Can find no vacuum leaks.

: The idle is erratic and a little slow @ 650 rpm, I think. Sometimes it has what appears to be a miss, sometimes it lopes, sometimes it sounds just like an intake valve is burned, sometimes it runs perfectly.

: Anything I can do to get the car to run a little bit rich helps until the computer overcomes the enrichment, then back just like before. New plugs did not help. Compression is OK and equal between cylinders. The car runs fine at higher RPM's.

: Leaky injector? dirty injectors? something electrical? O2 sensor works? valve adjustment?

: My local car guru can only suggest imperical parts changing in hopes of finding the cause by sheer luck. That could cost a small fortune even at wholesale, but I would have a nearly new car.

: Any help would be greatly appreciated.

: wjc

you probably have a bad icv idle control valve the computer controls the engine idle with this device and if its bad will cause some of the symptoms youre describing especially low idle speed and they are very erratic (depending on where it sticks).it's basicly a controlled air bypass past the throttle plates (more air, faster idle and vice versas)and the small motor that controls it can go bad and they also get gummed up from fuel vapors causing them to stick.if it sticks to far closed not enough air to idle properly(low idle)if it sticks to far open the motor gets to much air for the amount of fuel the injectors are giving causing what seem like a lean burn condition (surging and missing )and some times it sticks or works in just the right place.if you just did the throttle gaskets you probably saw the thing under the throttles (round tube with wires and two hoses coming out of it)that was the time to change it, much easier with throttles out of the way.by the way change the hoses to as they get hard and brittle and will crack causing an air leak.also check an make sure the throttle switch is working properly as this is what tells the computer to start controlling the idle using the icv when throttles are closed these also go bad or need adjusting.hope this helps Angus


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