Hi everyone, I'm new to this page, just picked up a 2000 jeep Cherokee 4.0 limited model. It's very clean!, but does have some things I would like to address. OK, so when i first went to look at my jeep, the dealer started it up, it hadnt ran in like a couple weeks so it was a true cold start. it ran good, then came down to running idle, then after a minute, it went into a rough idle mode, almost wanted to die, then came back out of it. Well i figured it wasnt anything big, water in the gas or something like that, I have gone through a tank of gas, no change. It's been doing it constant. like today, i started it this morning, got warm, then came down to running idle, then i shut it off. I went to leave today, went out started it and it went into that mode. I went to my buddys place, was there for an hour, then went to leave and it did it again, idling about 500-800 rpm when it does it and sounds really rough. If i try to give it gas it cuts in and out and lacks power. Then after like 2 minutes it comes out of it and is fine while its warm. Kinda weird. Not sure if its the IAC is bad or TPS. or just junky gas somewhere orrr. Idk not a HUGE issue but i want to address it. Oh, and I have completely gone through the throttle body and cleaned everything, including a new base gasket. Thanks in advance

 

Sounds like a leak of some kind, or a bad sensor. Being that it's newer than 1996, you should be able to hook it up to a scanner (most auto parts stores will scan it for free). Is the Check Engine Light on when it runs rough?

I would start with the basics like spark plugs, when were they last changed? how do they look? Look for frayed/cracked/dry rotted vacuum lines, intake tubing, gaskets, etc. Are all your ground wires clean and tight? Is there anything that looks broken or missing in the bay?

 

Oh, when I cleaned the IAC the whole nipple end came off when I was cleaning it, but I put it back in place. Could this be my problem? I haven't done much with plugs or looking for leaks but wouldn't a leak be constant rough idling? No check engine lights on. Thank you for the response.

 

I had the same thing happen last summer when I was on vacation for 2 weeks from work and did not drive my jeep. the IAC was getting a little slow from sitting, I took it out cleaned it and reinstalled it and it worked fine since then.

 

So you think i should try a new IAC?

 

I just re-read your first post. Try doing a test on the TPS and see were that gets you. Also check the map sensor mounted on the side of the throttle body. There is a small hose on the bottom that tends to clog with carbon. It also sounds like you are getting symptoms of heat soak associated with the 99+ XJ's. look at the #3 fuel injector there should be a metallic tape on it to keep the fuel from vaporizing after you shut it down, there a lot of write ups on different ways to fix it. Don't start replacing parts with out some testing.
Try disconnecting one injector at a time and see if that changes anything wile it is running like that, or get a stethoscope and listen to them wile it is running. You might just have a stuck injector. I hope this helps.