New member...interesting issue intermittently, drop idle, run rich

[hitman]

Ok, so I have this 99 Cherokee...4.0L 5 speed 4x4. It has approximately 117k on it (upgraded to the sport cluster with all the gauges...so that's pretty close.) When I got it at 85k, I did a complete tune up...plugs, wires, cap, and rotor. All were the original parts. Recently and intermittently, the Jeep will drop idle, run rich, sound like it's misfiring, not throw any codes, and generally make me upset. It REALLY sucks when it does this while driving. It then turns into "how many times can we make this guy hit his head on the headrest?" until I floor it and bring it above 3000rpm. Sometimes, this will cure it for the rest of the drive. Sometimes it just hates me and this process will take a couple tries. Without any codes, I'm kind of at a loss for where to go and was curious if anyone else has encountered this. Thanks for the help.

[bigjim350]

Sounds like the IAC could be sticking open. Might try taking it out and cleaning it or replacing it.
http://www.ehow.com/how_7524626_clean-jeep-cherokee-iac.html

[XJMJeep]

This one has pictures plus keeps it in-house :thumbsup:

http://www.xjtalk.com/showthread.php?t=10844

[hitman]

Thanks for the help guys. I'll take a look at that. I know I've got some cleaner kicking around so it won't cost me anything.

[Carves]

When are you checking for codes ... whilst the issue is happening or when you can access a code reader ??

Not all fault codes are kept in memory if the issue clears itself in a short space of time.

IAC is probably a good place to start ...

Anybody got any thoughts on a vac leak as the culprit ??

[4.3LXJ]

Any cracks in the exhaust manifold?

[hitman]

When are you checking for codes ... whilst the issue is happening or when you can access a code reader ??

Not all fault codes are kept in memory if the issue clears itself in a short space of time.

IAC is probably a good place to start ...

Anybody got any thoughts on a vac leak as the culprit ??

I don't have access to a code reader during the issue. I can get access to one, but was checking to see if this is common. My guess is it isn't.


Any cracks in the exhaust manifold?

For some strange reason, I don't have a typical cast iron manifold. I have a header looking unit. Did they come with headers in the later years? I doubt it was upgraded for performance before me. But, no, no cracks there.

[4.3LXJ]

Yes, the manifold is a header looking thing out of tubing and stamped steel. They can crack where the tubes come together and cause fuel mixture issues

[hitman]

Yes, the manifold is a header looking thing out of tubing and stamped steel. They can crack where the tubes come together and cause fuel mixture issues

Ok...I wasn't aware they made them out of stamped steel. I'm pretty sure the 91 Wrangler I have in the garage has a cast iron unit. But, no leaks there. Speaking of fuel mixture issues, is it possible my precat O2 is just getting lazy? I had to replace one of them (don't remember if pre or post cat) when I got it because it threw a heater circuit code.

[4.3LXJ]

It is a possibility. They can wear out, but if you have 40 thousand on that one, then it might be due.

[hitman]

It is a possibility. They can wear out, but if you have 40 thousand on that one, then it might be due.

Are these things notorious for eating them? I put in a Bosch unit...the same brand I use in basically everything without issue. Also...it's nearing my 30k mark...aren't these due for tune ups right about now? I'll feel like an idiot if it's plugs getting fouled due to normal wear.

[4.3LXJ]

If it is a bosch, it should still be OK

[hitman]

If it is a bosch, it should still be OK

I'll have more time to mess with it when it's no longer my DD at the end of the month. Then I can start scoping sensors and see what's up. Was really hoping it was a common issue that everybody with a Jeep had and didn't need to make threads about. LOL

[bluedragon436]

My 98 does something that sounds similar to what you got going on... but it only does it every now and again, I've probably had it do it like four times in the four years I've owned it... so never really worried about it on mine.... Like mentioned above I would def start with looking into cleaning the IAT sensor... and heck if nothing else do like I did when I was having another issue... hit up a JY and pull some sensors and try and swap em one at a time and see if you any of them rememdy the issue, and then if you really want you can swap it out with a new unit...

[hitman]

My 98 does something that sounds similar to what you got going on... but it only does it every now and again, I've probably had it do it like four times in the four years I've owned it... so never really worried about it on mine.... Like mentioned above I would def start with looking into cleaning the IAT sensor... and heck if nothing else do like I did when I was having another issue... hit up a JY and pull some sensors and try and swap em one at a time and see if you any of them rememdy the issue, and then if you really want you can swap it out with a new unit...

I thought about doing this as well. My parts XJ is a fully loaded 98 with a bad 4.0L...seized tighter than a drum. Happens to be the same vehicle I pulled the interior, overhead console, cruise, cluster, and other stuff off of. So, I do have some sensors I could swap...just in unknown condition. It's also an auto trans vehicle with the part time 4x4 transfer case. I have no idea what I'm going to do with either of those. LOL

[CherokeeNat.92]

Just remember, in a rich condition. You either have too little air or too much fuel. So you can check items on either side. It doesn't have to be sensor bad. If you didn't change your air filter for an extended period of time, it will cause a rich condition..just an example. So i would look over your your air intake system and make sure you don't have any restrictions. then check the fuel. Could be a leaky injector.