rough idle and hesitation?

I recentley got my first jeep a few weeks ago and yesterday I took my kids to school in the morning and everything ran perfect, go to pick them up in the afternoon and while waiting for them to come out it started to idle rough. While driving home it had a hesitation when accelerating. Well to complicate things I went out to drive it around last night it was fine again!! It recently had a full tune up done and the air filter cleaned and oil(k&n kit). Any ideas on what could have caused this? I have gone over the typical stuff and everything seems fine, I did notice in chiltons it said to check timing, its a 94 4.0 so is this done by the computer or still with the dizzy? Thanks and please pardon my lack of knowledge with this motor other then what chiltons tells me to look at

run a can of seafoam through it and clean out the intake as well. run another can through the gas and see if it gets better.

and posting stuff like this in the OEM tech forum will generate more hits.

Thanks, I just ran injector cleaner threw it 2 tanks ago, so it can't hurt to clean the intake out either lol. Is there a way to move this to that forum?

If a mod sees it they can take care of it. You cannot do it as a user.

KingCopa,

You may want to check out my thread, sounds similar.

http://www.naxja.org/forum/showthread.php?t=1009441

put the seafoam in the throttle body it is awesome stuff

Base timing is set by the computer.

Assume there are no check engine lights or have you seen one? If so, pull codes.

Did your full tuneup consist of plugs, wires, distributor cap and rotor? If not, I'd recommend finishing the job. Failure to do so can result in the "chasing of ones tail".

Testing fuel pressure at the schrader valve on the fuel rail with a fuel pressure gauge is never a bad idea. Compare your numbers to factory spec.

Testing your throttle position sensor would be the next step.

My 2001 does the same thing once in a while. When I start it and its cold it starts and runs fine. But sometimes after its been running a while and I shut it off for a short period of time, after re starting it will lope and I'll get hesitation until I get to higher RPM. Last week it did it bad enough to Generate a CEL (check engine light). It didn't stay on long enough to get it scanned though.

I've tried numerous different injector/fuel system cleaners and cleaning the TB. I haven't checked my fuel pressures, and the fuel regulator/filter unit has crossed my mind.

I've got a 2000XJ that does/did this. There is a TSB out from the dealer that explains how to fix it. Its TSB 18 031 03 and uses PN 56028371aa. Whats happening is that injector #3 gets overheated from the exhaust manifold and starts to boil the fuel causing it to vaporize. This causes poor or no fuel delivery to that cylinder and makes the engine miss/stumble. The PN is a tin spark plug shield that they say to install around the injector to stop the overheating.

I did something a bit different than a tin shield with an old piece of header wrap and a ziptie and so far its working fine. I might actually do all the injectors just for the heck of it.

Edit: It also wouldn't hurt to make sure that the debris shield recall is done. There is a tin shield that the dealer installs over the top of the intake to keep junk from collecting on the intake and causing a fire. This is a recall item and was free to have done by the dealer.

would you happen to have a picture or how you wrapped the header?

he just wrapped a piece around the injector. If you want to do that, most parts stores sell heat sleeves to protect stuff. They are on the performance aisle. Just unplu everything, slide them on, then plug it back up

Pretty much like wolkpackjeeper said, I just took a small piece of it and wrapped it around that one injector to see if it made a difference or not. I didn't want to spend alot of time messing with it only to find out that it didn't fix it.

I read a few other posts on here that guys were also doing the #4 injector which makes sense considering that the #3 and #4 injectors are directly over the pre-converters in the exhaust. Some of the guys are also saying that going to NGK spark plugs helped clear it by but I'm not seeing how changing an ignition part is going to clear up a fuel delivery issue.

There is more than one option to fix this. Even just an old set of plug wires, cut one of the straight boots off the end and cut it to fit around the injector. They can definately take the engine heat and best part is they are free after a tuneup.

the spark plugs could come into play because the NGKs are generally a better plug, so they may have been getting a more complete combustion, leading to the O2 seeing less oxygen, leading to a different duty cycle on the injector.