Hello all...It`s been awhile since I`ve updated on this thread and thought some of the guys who were helpful may have wondered what became of it..And maybe some new people can go back and read the original post and have some input:

I switched my instrument cluster out so now have a temp gauge to look at and am now not so sure the problem is heat related...The check engine light will still pop on at the same times..15 minutes or so in stop and go city driving or if I get right on a highway I can drive for an hour and it won`t come on untill I get off the first exit and stop or go off a side road and slow down...BUT I did notice recently that a few mornings when I was in a very tight parking space and had to do a lot of slow back and forth twistings and wheel crankings to get out the check engine light came on even though the engine hadn`t gotten to hot yet..Another new thing I noticed which steers me away from the temp angle is that if I start the Jeep and let it sit and idle the check engine light won`t come on no matter how hot it gets but as soon as I put it in gear and start driving it comes on.

I disconnected the alternator totally and drove my usual rountine and that didn`t effect the timing of the TPS/check engine light appearing so that ruled that out as the problem..I also replaced that plastic Cam Position Center thing in the distributor but not the distributor itself and that wasnt it (I did notice some side to side movement of the distributor shaft when I took the cap off so will go back and investigate that)..Cleaned all the grounds I could find..That`s about it for now..I got one of those 99+ intake manifolds and was gonna install it but figured I`d wait til this TPS/check engine problem gets fixed

 

Check the harness where it crosses behind the engine. Lots of them have fallen out of the clips and lay across the rear head studs. The head stud melts through the corrugated plastic covering, then rubs through the wiring for all the goodies on the intake.

When I get a 4.0 liter in the shop with ANY intake-mounted sensor or injector issue, that's the first thing I check.

 

I think I`ve trued about everything to fix this problem and have decided to just live with it but want to give one last piece of info I`ve noticed in the hopes it may trigger some light to come on for someone....I have noticed a couple of times recently if I am in a really tight parking space (You have to parrallel park on my street and there`s not much room) and I have to really turn the wheels and edge forward and backward a lot to get myself out it makes this check engine light/TPS sensor problem come on...Can anyone think of any sort of sensor or anything that might be activated in that situation specifically?...As always thanks for any input

 

do you have cruse control

you my have a clock spring problem in the steering coulomb

 

Also, you said that the problem occurs in traffic, getting off the highway/getting into the city and parallel parking?

Out of the box idea:
I think something in the steering column may have something to do with it. When im in traffic, i tend to change lanes alot and turn alot(sometimes just back and forth due to boredom) city driving requires alot of turning too. Does it happen only when you turn the wheel past a certain point say like 45*? I'm def. no mechanic and def. wouldnt be able to help other than throwing out an extremely random idea that the above poster gave me... lol

 

Generally as a rule the check engine light pops on and the Jeep starts idling erratically after say 15-20 minutes of stop and go city driving ..If I can get on the interstate I can drive for over an hour and it won`t come on until I get off the first exit and slow down or stop...If i turn the Jeep on and let it sit and idle I will idle without the check engine light coming on for an hour but as soon as I put it in gear to drive it comes on and now the parking situation...The Jeep runs and drives perfectly until the check engine light comes on and then it starts the surging and rough idle and shows a Throttle Position Sensor code even though there`s nothing wrong with the TPS..I`m thinking maybe some other sensor is trying to send a signal when the engine rpm/speed/temp does something and it`s somehow using the TPS as it`s ground source making the computer think the TPS is bad?..Or perhaps the computer itself is faulty and sending the wrong voltage to the TPS?..Or it`s a poltergeist

 

Def. a poltergeist... has to be... lol

 

I was reading a post last night on another topic and someones answer got me to thinking if this could possibly be my problem....Not long ago I noticed I have a hairline crack in my exhaust manifold right at one of the points where 2 of the tubes come together..It pretty much goes completely around but is at a place where the exhaust tubing is still held together...I am now wondering if it`s possible that as the metal gets hot and expands this crack gets just enough bigger that the fresh air seeping in fools the oxygen sensor into thinking the gas/air mixture is wrong and somehow this is causing a problem with the TPS as it thinks everything is fine or maybe even the O2 sensor is sending out a signal which using the TPS sensor as it`s ground source or whatever

 

Keep us up to date on what you find out. Your problem sounds alot like mine and I have just started down the replacing sensor path of pain. Same thing, I can drive on the highway forever but a bit after I hit the city is when it starts. I might have missed it in your forum but someone has mentioned to me the Ignition Control Module switching to high temp mode and causing it. I'll let you know what I come up with if anything. Went to auto zone to get my codes pulled but they said they don't do ODB I cars so gonna have to get a diagnostic, I'll let you know the codes and see if we have the same problem. Good luck!

 

OK..So I was looking over the wiring diagram for my Jeep last night trying to puzzle what all is connected and noticed that all the main sensors (TPS, CPS, CTS etc) share a common black/light blue ground wire and they all seem to lead to something called the Transmission Control Unit... My latest observation with my Jeep is that once the Check Engine light kicks on at a certain temp in the morning even when I go to work and park it for 5 hours and it cools down when I go out for lunch as soon as I shift it into Reverse the check engine light pops back on (If I start it at lunch and just let it idle the light doesn`t come on)..So the act of simply shifting into R does something electrically that makes the check engine/TPS problem appear..I`m wondering if this "Transmission Control Unit" is somehow involved either by being faulty or by being a bad ground source?

 

http://www.go.jeep-xj.info/HowtoEngineInstall4.htm found this on one of the go jeep threads on how to reset the computer,dont know if it well help,just thought you might try it,did mine to get rid of some old stored codes.

 

Thanks..I`ll try that before heading out tomorrow..Someone told me to touch the positive cable to a ground before but this link seems to list a few more steps

 

My check engine light has been on, and stays on. Its been this way for 4-5 years now. The scanner shows O2 sensors and I have replaced both of them with no change. I noticed about a year agao I have a crack in my exhust in the same place you mentioned. I just got done coating the crack with a huge globe of JB weld. I hope this fixes the problem cause I really don't want to take the intake and exhust off. I would weld it but it is so tight I cant reach it.

I just found your message about the exhust interesting cause I have the same crack. I have heard that the mainfolds are very prone to cracking.

 

Let me know how it works out..I can see how a crack there might fool the O2 sensor into thinking somethings wrong..After a lot of making notes and experimenting the past week I`ve come to conclude that my problem might be some sort of grounding problem since so many things seem to set it off and all seem to be sensors that share a common ground..If the weathers good this weekend I may start tracing everything and looking for some sort of hidden problem

 

Well, I put a big layer of JB Weld on the exhuast crack. I don't know if it just needed to cure overnight but after several hours I drove to the gas station. Needless to say I had smoke pouring out from under the hood. The JB weld stuff turned black and the crack reappeared.

I really don't what to replace the header since I would have to take off the intake as well. I guess since that I have had this problem so long I might as well leave it alone. It really hasn't caused any problems other than that darn CEL staying on. The engine runs just fine and I do tow a trailer quite often during the summer for mowing.

It is my only vehicle so I really can't take it out of service for a problem that doesn't cause any issues. I guess if it ain't too broke don't need to fix it.