High idle

Latley when I start the engine it revs up and idles in the neighborhood of 2000 RPMs. It doesn't always do this but usually does. It almost always drops back down to a normel idle level after just a couple of minutes of driving. It seems like a sensor problem to me but I wouldn't know which one. It's an '89 4.0 with just shy of 200K miles.

Just a thought:

Check the condition of your vacuum hoses. Sometimes tiny
cracks can expand and "self-heal" by the heat of the engine.
I had that happen in a previous life (pre-XJ). Replaced all the
hoses and bingo - problem gone.

Good luck!

Clean the throttle body really good. Take it out, clean it down. use an old tooth brush to get into every crack you can with the cleaner. Reinstall go as new. You can also have the sensors checked out. TPS, MAP, Idle stepper motor, but clean it first this is most likely the problem.