my bmw sounds like it is surging when idling, seems to get worse when it warms up. this happens from about 700 to 1400 rpms. my mechanic can't figure this one out. thank.
idle surges on 1990 BMW 325i
It is the (ICV) idle control valve or its connections to intake air duct
Its the Air Flow Meter. Its a black box the size of a deck of cards on the intake side of the throttle body. This is glued down but you can gently pry it off one side at a time. My 1990 325I worked fine until I removed the power side for inspection. I did not reinstall it properly and the vehicle now surges up and down like yours. I plan on reinstalling it properly soon. It could be the cable to the unit. It surges when unplugged. Google Bosch 0280202082