m20: straaange idle issue

[Sasquatch440]

alright guys, ive got an 89 325i that took a 3 year hiatus to rebuild some things.

after about a week or so of driving, when i come to a stop or just let the car sit the idle will be around 500rpms. now, if i get out of gear and coast to a stop it will stay at 650 for about 5 seconds then drop to 500 again. i can coast the car for an infinite amount of time, but 5 seconds after i stop it will drop to 500.

what would cause this?

all new hoses, tps correctly adjusted, afm working, iac working, and no vacuum leaks. stock ecu no chip

[Idrisu]

I've got the same problem. Bump.

[M3llOW]

This is most likley linked to the MAF check with barest.com they have great refurbished parts

[Sasquatch440]

still havnt figured it out

[YosemiteSam]

Have you checked your IAC?

[jlevie]

My guess would be an intake leak, flaky ICV, or bad MAF in that order, assuming the TPS is good and correctly adjusted. The only sure test for intake leaks is a properly executed smoke test using a pro tester. I'd start there.

BTW: the correct way to adjust the TPS is to disconnect the ICV and adjust the throttle stop for 950rpm on a warm engine. Then adjust the TPS so that the idle switch closes 1mm off the idle stop. When the ICV is reconnected the idle should be 750rpm. Note tat early DME's (before the 173) were notorious for erratic idle.

[Sasquatch440]

update: i changed the chip in the cpu, and it fixed it.