Volvo: Volvo 940 erratic RPMs, volvo 940, wire harness

Question
My Volvo is having problems again. I adjusted the TP switch, cleaned the throttle and IAC valve, checked for codes (there weren't any) and STILL there are problems! For the most part, my Volvo is still idling too high (at 1600 rpms) but I've noticed that at start-up it idles at the correct rate but slowly goes up to 1600 and every few minutes the rpms suddenly drop to 1000 but go back up to 1600 again. Also, while I'm driving, the rpm needle dros sharply to 1000 but picks back up to 1500 and steadily drops to 1000. Is this normal?

Answer
Yochwa,
You have done all the normal things that can be done. Now you need some diagnostic tool to take reading of the sensors. The Volvo VST will hook up to the control unit and give reading of those different sensors. You want to look at more specfictly the fuel injection temp senor and compare it to book values. It might be time to get a Volvo shop to help. Also check the wire harness for schafing wires that might be shorting out.