Check engine light. Code 1215.
 

Hey guys. Finally got the 1991 325ix started and now it idles and runs pretty good. A little rough on cold starts. My problem is this. When I let the car sit and idle the check engine light comes on and it's the 1215 (MAF) code. If I take the car around the block the light goes off, but as soon as I pull back into the driveway and let it idle the light comes back on. Could it be the Idle Air Control valve, or does this have it's own motronic code? I just replaced the MAF with a remanufactured one today, so I'm pretty sure that isn't the problem. Any thoughts? My IAC hums when I turn the car on, is this normal? Also, does anyone have a list or diagram labeling all the relays on this car, I can't find one anywhere, and I don't have a copy of Bentley's yet.

Not familiar with your model, but when the car is shut off, can you hear the throttle position sensor switch click when you reach down and open the throttle on the throttle body? Computers have a hard time correctly diagnosing a failed TPS when they don't get a closed throttle signal. If you have an ohm meter, unplug it and see if it is switching as the throttle cracks open.

Is IAC the ICV (idle control valve)? Yes, they humm.