Rough Idle & Stall While Stopped

Question

Make: BMW

Model: 535 IS Automatic

Year: 1988

Miles: 230K

I have a very similar problem to (Automatic: revs dropping then stalling when stopped at lights) The car is fine in just about every instance except when it is standing still. Then it tends to stall out and idle hard at any location where it is stopped. The car has been taken to a dealership, and a general tune-up was done and the distributor caps were replaced, also, the pressure on the Fuel Pump was also checked. I wouldn't exactly say that I trust these people though. They weren't able to find the problem after a month and a half and returned the car in an unprofessional state. The wires for the brake lights were exposed and weren't even attempted to be covered. That and they said that they fixed the problem, but the car idled hard literally the first time I tried to drive it out of the parking lot and stalled at the next light. I'm just curious if there was anything I could try.

The car exhibits this behavior when both cold and warm, and occurs at initial startup for the day, and after driving around for a bit. Other than that you would think it's just fine, then it stalls out at a light. Strangely enough, it always starts up immediately after throwing it into neutral and starting it back up after a stall.

Similar to the earlier poster I'm not a mechanic, but I'm curious if there were a few things I could try before taking the car to the stealership (Or a different one).

Answer 1

I would check the idle air control valve, or the IAC.

This might likely create the exact symptoms you describe. Determining if it's working properly is a bit of a chore for a DIY person, but this is where I would start.

The part looks about like this:

And I think was located about here on an '88, behind the Vane Airflow plugged into the checkboard intake tube:

You can take this off and spray it out really well with carb cleaner and an old toothbrush to see if that helps. They can be full of the nastiest black carbon gook that would rival the tar pits of Jupiter. They are cheap enough to replace (maybe $50) if cleaning doesn't help. Electronically diagnosing proper operation on this part is complex, but should be easy for any reputable Euro mechanic. Any decent mechanic at all, in fact...

They usually fail from carbon sticky crud, not electrical failure.

Hope that helps and Good Luck!