Strange idle problem

[B1mmer]

I've got a strange idle problem I'm trying to diagnose. I've got an '01 GT-S 6spd with 47k mileage. Basically, the car idles perfectly when the car is stopped. Right at 800 +-50 rpms. When I get the car going 40+mph, and depress and hold the clutch in or put the car in neutral, the rpms will drop to normal idle speed, and then it will fluctuate between 800 rpms and 0 rpms intermittently, until the car comes to a complete stop, and then it will idle perfect. I noticed the problem about a month ago driving down a hill and I got lazy and put it in neutral.

The car has stalled like this about 3 times, so it's not just a guage issue. I went to the dealer and talked with a tech, and he hooked up an OBD-II sensor, and the ECU didn't throw a code. I then took him for a ride and showed him the problem, and he was stumped. An insight?



My thought are:

1. Speed Sensor?
2. Throttle Position Sensor?

The only problem with the TPS is that it shouldn't idle correctly while motionless.

Thanks, Aaron

[B1mmer]

After doing a lot of testing, it turns out that my Mass Airflow Sensor was dirty. I must have over oiled my K&N, so I pulled the K&N and cleaned the lower and upper part of the airbox. Then I pulled the MAFS and cleaned it with brake cleaner. Re-installed and it was as good as new. - AB