inconsistant idle on cherokee

[jeep guy]

I have a 90 Jeep cherokee with a 4.0L. The idle starts out at approx. 700rpm then gradually works its way down to about 200rpm. Then the engine surges back to 700rpm and the process starts over again. It seems to do this both hot and cold. The truck has a new alternator, TPS, MAP, O2 sensor, antiknock sensor. Has anyone else had this problem or know of a solution! IDEAS! thanks in advance.

[Christopher]

Start looking for a vacuum leak!! Check ALL of the plastic lines as well,especially the ones by the battery that go into the vacuum canister behind the R/F corner of the bumper.These have a tendency to get eaten away over time by battery acid,and the other lines get heat damage and crack over the course of normal usage.

[karl]

Along with the vaccum lines, one other thing could cause this problem. Check and clean the Idle Air control valve. I ,my wifes car, have a 90 cherokee that had the same problem. I have found that cleaning this part about one every year cures the idle problem.

[jeep guy]

Thanks guys for the info on the idle. The IAC valve was replaced about 8 months ago. Is there a way to test this to see if it is faulty? Meanwhile Iwill check the hoses by the battery. The rest of hoses on the left side of the engine are all new. Would the lack of a catylitic convert. cause any problems due to backpressure, or would these be minor. Like a slightly lower idle, but not inconsistant.