It seems my 1995 940 non turbo sedan is a bit tantrum prone. Sometimes, if the car is in idle the rpm's will dip almost to 500 and will eventually return to 750 which I believe is the proper rpm. This usually happens with the a/c turned on. No check engine light comes on.
MILEAGE ON CAR IS @135,000. one mass air flow filter contact was a bit rusty and cleaned.

 

This is normal. When the A/C comes on, there's a drag on the motor caused by the added load, then the computer compensates for it, idle goes back up...