1991 740, 157,000 miles
You will recall that when cold, the engine would start right away, but there would be no fast idle. And also there was a second problem--once warmed up, the engine would idle in N or P at about 1500 or jump between 1000 and 1500, instead of the normal 750.

I cleaned the idle control valve, as many of you recommended. That didn't help either problem. I then decided to work the problem using a basic logical scheme. I thought that if the idle control valve is not being activated, maybe the coolant temperature sensor is the problem. I bought a new sensor for $21, put it in and like magic, both problems were solved (cold and warm idle problems). I am not a mechanic and was amazed that by simply replacing the sensor the problems went away.