I have an idoling problem with my 1990 cherokee limited. it will idol normal for about 5 min or so then the idol will up to 1500-1800 rpms. I changed the IAC. should i change the TPS? Shouldnt there be a check engine light that goes on if theres a bad TPS? I would greatly appreciate some help here before i dump some more money into this truck. i luv the way it handles in the snow though =)

should i try a tune up too?

should i try a tune up too?
I have been struggling with the idle on my 90 4.0 with out a lot of success. I had the tps replaced 10k ago and it helped till now. The inline 6 with MPI has mutiple sensors that all work on fuel and air mixture and apparently you have3 to be smarter than me to figure it out. My jeep does not have a check engine light so I don't know how you get the codes. Tune ups usually help but check wires and plug first to see if you need to spend the money

thanks for the info. i will try to figure something out,as i can not bare the high idoling =(

I had the same problem you are having replaced all items you mentioned in the end it was the intake manifold gasket. Took me forever to figure this out.

Good luck

sounds like a vacuum leak, just as
"BLKLT4" said, i would check for vacuum leaks. Could easily be your manifold gasket.

Vacuum leak somewhere gets my vote too. There are a lot of hard plastic vaccum lines, especially around the air box. Check them and make sure none are broken. If so, you can "patch" them with some small neoprene tubing.

Oi! Have the same problem in my -89. Replaced intake gasket (which is a bi*ch to do) but problem is still there. Idles extremely rough when in op.temp. Flutters between 400-1200 RPM when idle. Cleaned TPS, housing, everything is new stuff from the sparkplugs all the way to the ignition module. New airfilter, new gasfilter...phew, starting to run out of breath... Going to check for vacuumleakage tomorrow. A spraycan of "starter gas" and spray around vacuumhoses and tubes when engine in idle. If revvs change when spraying, U have found youre leakage. If anyone have any ideas, please help!!!!

It might sound rediculous to you guys but grab a volt meter and put from your engine block over to your negative side battery post if it is more than .2 volts put a new ground from battery to black and then take off negative side cabe and clean at battery and where it goes to ground at. This is where your ecu gets its ground and when it has trouble finding ground it will act funny just like this. Also try a top engine clean also know as taking your intake off and shoting water slowly into the throtale body this will clean carbon deposits from your engine. keep me posted

water? had not heard that one

yes just think about it when you have a bad head gasket think of how clean it is inside that cylander this is the best top engine clean