i have a 1990 cherokee 4.0 some times when i start it the idle will go to 2000 rpm when i drive and let off the gas the rpm stay foe about 2 to3 seconds and if im on a trail at just above idle it will surage in rpms help pleas

No check engine light? My cherokee did the same thing but it threw a code so I had it checked at autozone and it ended up being the Throttle Position Censor.

Moved to Cherokee Chat so you should get more response here.. The builds section is strictly for documenting the buildup of our jeeps..

The most likely culprit on your 90 is the IAC but thatcan be cleaned but be careful not to injure the pintle while cleaning. The second most likely is the TPS and on yours it will need to be adjusted if it is replaced. and the third possibility is the O2 sensor.