I've had my '96 XJ since last November and occasionally it'll start to idle pretty rough and throw a misfire code, but then it goes back to normal in a few days. It starts misfiring after I've been pushing the engine pretty hard, but only runs rough when it's idling. The issue goes away when the engine speed is above 1000RPM. Since I first had this problem I've replaced the plugs, cap, rotor, wireset and MAP sensor. I would scan it to see exactly what code comes up but in CA it's illegal for autozone to loan code readers out to people. The interesting thing is that when the CEL blinks out the codes, code 43 (one or more cylinder misfire) comes up twice and I read that they are not supposed to do that. Can anyone shed some light on this?

 

TPS will cause the prob. you are describing. I've been through this 2 times,and have resolved it with a new TPS.

 

Thanks. Is there any way to test the TPS? I replaced a perfectly good MAP sensor because the test I did was wrong, and those things are freaking expensive.

 

I just found a test for that on AutoZone but I think I'm going to replace it because some of the other symptoms (such as hesitating on acceleration) happen too so I'm pretty sure it's the TPS.

 

I've read cases like this and you got it correct, a new TPS would absolutely solve your problem.

 

Had this same type of problem, your jeep dealer sell's a carbon cleaner it was 6.50. i have 220,000 miles on my Cherokee 2000. It cleaned the intake and it is working great. Here is the article that I found hope this helps:



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Question

I have a Jeep 2000 Cherokee Sport. 145,000 miles. One owner, me! Trouble with cyclinders missing when first started if jeep has been run and stopped a few times. (Like doing errands). When cold or has sat for 45-60 minutes, no problem. On long runs I have no problem when I stop for gas and then start back up. It did this last summer and I changed the plugs and eventually the coil pack. The first coil pack (china made) was bad and I had to replace it. It has run good for 7 or 8 months and now back to doing the same thing again. Any suggestions??

Submitted 100 days and 6 hours ago.
Category: Jeep
Value: $9.00
Status: CLOSED



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Accepted Answer

great jeep

there is a few issues it could be... the most common and the starting place is a complete and very good engine decarb....

what happens is the intake and exhause valves get carboned up on the jeeps and this causes the vavles to stop spinning in the guide.. this cause the valve not to seat properly causing a miss fire.....

the chemical is 9.00 at you jeep dealer and it is called combusion cleaner....
i have had to run this on some high milage jeeps 2 or 3 times depending on how bad it is carboned up.......

start and drive the jeep and get to operating temp..
remove the air horn boot off the engine and start the engine..
hold the throttle at 2000 rpms and spray the chemical directly into the opening on the throttle body...... spray 2/3 of the can and than shut the engine off .
hold throttle wide open and spray the remander of the can into the throttle body..
reinstall the air horn boot and let the jeep sit for 2 hours...

start the jeep andit will be hard to start.....
hold throttle wide open and start the jeep and when it starts clearing out let the jeep idle..
test drive the jeep several miles. ( it will smoke badly the 1st few miles)
and than it will clear out and be back to normal;....
again i have had to do this 2 adn 3 times on some high milage jeeps. ....

this will clean the intake the valves and piston and clean out the exhaust.....

this needs to be done every 6 months on a 100k , milage jeep....
this is a common problem and repair for the jeeps......

let me know if this helps...

 

A "decarboning" is pretty effective on high-mile 4.0's. Just remove and clean your plugs afterward.

What kind of plugs did you install?

 

Another thing to check is the condition of your injectors and injector wires. I just had this problem on another car...went through all sorts of similar measures. Turned out that some how, an injector wire had burned out (got really high resistance using a multi-meter). replacedthe wire and problem solved.

 

I put in Bosch Platinum plugs because it was the first time I ever worked on a car and I didn't want to have to worry about gapping them. It had the same problem with the champion truck plugs in it. I'm going to replace the TPS this weekend and if that doesn't work I'll try to decarbon the engine, it's kinda high milage, 148,800. I did see some carbon buildup on the throttle body when I was inspecting it if that helps diagnose it. Would a bad TPS also make me get bad gas milage? I get about 12 but that's around town and some freeway driving with atleast one bike on top.

 

Okay so I replaced the TPS and it runs better, but still throws a code about 45 seconds after I start it up. The idle is still off but it's not as pronounced. I'm hoping it'll just go back to normal like it has the last 4 times this happened, but I also want to make sure it doesn't happen again. I'll do the carbon cleaner thing when I have time to run to the dealer.

 

Bosch plugs= junk, at least in a jeep motor. all you need is the dirt cheap champions, and from the extra few bucks you saved you can pick up a gap tool, its not that hard to do