Another M20 idle problem...
 

My 86 325es is having a weird idling problem. It starts up and idles fine for the first couple of seconds...then it jumps up to ~2000rpm then down to below 1000...and continues this weird cycle. The engine is not very responsive when I step on the gas. It lags and sometimes doesn't even respond to the gas pedal. The throttle plate clearance is set at ~.0015 inch, The throttle cable is fine, there are no noticable vacuum leaks, and the throttle position sensor is fine. The AFM was sticking and took a while to close at first, but I sprayed some WD-40 to free it. Can it be the AFM, is there a way to test it? How about the ICV. Or is it my Motronic computer unit?

99% sure you've got a vacuum leak somewhere....

check the valve cover gasket....

I hope you're right Jared because that would most likely be an easy fix. I will thoroughly investigate the car when I get home today.

Hey Jared, YOU WERE RIGHT!!! The crankcase tube that connects to the underside of the intake manifold failed to provide a complete seal. If I positioned the tube furthest up, the crankcase end exposed a vacuum leak...if I positioned the tube furthest down, the intake end exposed a vacuum leak. My NEW question is...how can is solve the problem?

By the way, I came upon this discovery when I installed (duct-taped) my vacuum cleaner hose to the the intake boot....

You'll have to take the intake manifold off in order to change the two O-rings at the top and the bottom. Sorry you have to undertake such a job in order to fix something so trivial..

I would suggest possibly bead blasting the manifold while it's off to clean things up as well as replace all the vacuum hoses while you're at it.

In order to remove the intake manifold, you'll need to remove the valve cover, fuel injectors, fuel rail, throttle body and the air boots.