OK, I just got through fixing a stall/no start at operating temperature problem (crank sensor lost resistance at temperature) on my 94 940 non-T w/ Rex/Regina when this problem reared its ugly head. It mimics a carburetor with a sticky throttle. From idle (around 800 RPM) if the throttle is increased slowly to just under 1500 RPM and released, the RPMs will drop normally. If the throttle is slowly increased to past 1500 RPMs, it will drop to 1500 and stay there, if slowly increased to past 2000RPMs, it will stay at 2000. From idle, if the throttle is goosed up to around 2500 RPMs it will drop to 1500, and stay there or slowly creep up to 2000 RPMs. If the throttle is goosed to around 300 to 3500 RPMs it may drop to 1500 and stick, or it may stutter at 1500 for a half second (as if having second thoughts), then drop to normal idle. This happens even if I an actuating the throttle by hand from the engine compartment, and closing it by hand firmly. The TPS passes tests, the throttle body was cleaned recently. When the problem with the crank sensor must have been beginning, I was plagued with what I call a "hunting" idle, the engine RPMs would surge and drop at start up, until I placed the car in gear, and drove away. I have run all of the diagnostic functional tests, and all of the components passed. I also tested most of the components while diagnosing the crank position failure (either by part swap-out, with a multi-meter, or heat-gun stress testing). I am stumped (A phase from Myth Busters comes to mind:"...when in doubt, ... C4!). If anyone has any thoughts (other than vacuum leak, that was tested) it would be greatly appreciated. Thank you for your time.

 

Start by cleaning the Idle Control Valve, under the throttle body...