Here we go!
Ok, was able to do a little reading in the Bentley Service Manual today (get a copy if you don't have one). On page 130-20 it talks about how to test your idle speed control valve. From the symptoms that you have told us, it sounds like this could be your problem. Here is a small section from the book:
Idle control valve, testing:
Idle speed is maintained by the ECM through the idle speed control valve. The idle control function compensates for engine load and engine operating conditions. Idle speed is adaptive through the ECM and no idle speed adjustments can be made.
Before testing the valve, confirm that the throttle position sensor is working correctly.
The tests given below are electrical checks only. They do not check the mechanical operation of the valve. If the valve is suspected of causing poor idle, substituting a known good valve is the best way to check for a mechanical fault.
1) With engine running, check that idle speed control valve is buzzing.
2) Turn on A/C or shift car into drive. Idle speed should remain steady or increase slightly.
3) If valve is not buzzing, or if idle decreases in step 2, stop engine and disconnect harness connector from valve. Check resistance of valve across its terminals. See Fig. 30. Test values are listed below.
Idle Speed Control Valve Resistance Values:
- M50/S50 US engine
Terminals 1 & 2 20 +/- 5 ohms
teminals 2 & 3 20 +/- 5 ohms
teminals 1 & 3 40 +/- 5 ohms
I can't seem to get a copy of fig 30 to post. If I can get that worked out I will. It basically says that when you are looking at the valve as it is mounted in the car, terminal 1 is on the right side and terminal 3 is on the left.
Hope this helps!
1997 E36 M3 - running stocker style right now...