This post will be a bit long but I don't want to miss any info which might cause someone to put their finger on the trouble:

Hello all..I have had this problem for almost 3 years now and will say upfront that pretty much anything anyone suggests I have tried so I'm looking for some real "outside the box" ideas..So here we go...Almost 3 years ago my right side motor mount broke on the side where it attaches to the motor..I mean all 3 bolts sheered clean off..Needless to say the motor dropped and the only thing that kept it from going down to far was that the bottom of the distributor came to rest on the part of the mount still sticking out from the side wall..It happened way out in the boonies and I had to get home so I babied it back as best I could but there was some up and down banging of the bottom of the distributor but nothing really hard..The distributor is held in with a pretty hefty bolt and I didn't notice any upward movement of the shaft ..Now this might not have anything to do with the problem I'm about to describe but the problem seemed to appear shortly after this so I figured I'd better include it just in case...
Shortly after this event I noticed that my "check engine" light was coming on and when it did the Jeep was running roughly..I checked the codes and got the code 24 "Throttle Position Sensor"..OK..Long story somewhat shorter I tried 3 used TPSs from Jeeps at the junkyard and none of them fixed the problem but I did notice an interesting pattern to the problem..It seemed the check engine light coming on and the rough operation only happened when the Jeep warmed up to a certain temperature..If I can get on the highway I can literally drive for hours and the check engine light won't come on..But as soon as I pull off the first exit and come to a stop it appears..If I am driving in stop and go city traffic the problem appears after about 15-20 minutes of driving...So it appears the problem is engine temp related..Always the same..Jeep drive perfectly then warms up, the check engine light pops on and it begins to struggle and run rough...Always the same TPS code.
To date I have replaced the TPS 4 times (3 used and finally a new one)..Replaced the electrical plug for the TPS..Replaced every sensor even slightly related to engine temperature or anything else (Oxygen sensor, Knock sensor, Coolant Temperature Sensor, MAP sensor, Manifold Air Sensor,TPS sensor, Crank Position Sensor...)..Also cleaned up a few grounds...

So that's about it in a nutshell..Jeep runs perfectly..Can drive 150 miles on the highway with no problem untill I get off the highway and stop/slow down...but in the city only 15-20 minutes..Check engine light comes on..TPS code..Runs roughly..My latest theory is that the TPS and the coolant temperature sensor share a common ground wire and for some reason something is wrong and when the CTS gets to the point that it kicks in it tries to find a ground source and not finding it`s normal one it uses the TPS as it`s ground and causes a problem there..Does that sound plausible?
I`m sure I left out some info so may need to post more as suggestions come in and I recall trying stuff..I`ve just come to accept the problem as a quirk of my Jeep and gotten to live with it but everytime I drive my ex somewhere and that check engine light pops on and it starts surging and idling rough she gets nervous and harping about getting a new car so i`d like to get rid of the trouble once and for all..Thanks in advance

 

For me the purple text is a little hard to read, took me twice as long to read as it should have. Sorry, I don't have any ideas for your problem.

 

How are the ground wires on the passenger side of the engine there should be 2 near the alternator, I would disconnect the battery and check the resistance to them from the battery. Also I would load test them with the brightest most powerful light bulb you can find they need to be 100%. I would also remove the distributor cap and check for side to side play in the distributor shaft if it moves the bushings in the distributor are worn out and needs to be replaced. There is also a ground on the back of the engine held on by a 18mm nut to the rear most head stud. What is the TPS reading when it is acting up?

 

Replace the distributor with one out of a juck yard. That could be the problem right there. While you are at it put a 180 thermostat in it to get the motor to cool down some, from the factory operating temp and see if it still does it.

 

I know this sounds crazy, but what you describe sounds like RFI/RMI (radio magnetic interference/ radio frequency interferece) coming from your alternator. this can disrupt the "hall-effect" communication between the pick-up in the distrubuitor and the Crankshaft Postition sensor.

Do one thing for me: disconnect all electrical connections from the alternator. There's two fuses you can pull, but I've seen alternators make 28 volts with no power coming to it. It's like it was a pure dee generator. It's cause the regulator inside got fried into one position. I know it's gonna take some time to get under there, and I also know that you don't want to go driving around forever with your alternator disconnected, but once you've disconnected it, see if it still runs like crap at a certain point in the drive. The test is free, after all.

Have you checked into that little porcilen coil resistor lookin thingie over on the driver's side fender close to the firewall? This would have more to do with fuel pressure.

If the TPS is a three wire sensor (and I'm pretty sure it is), you have power coming into it, ground, and power coming out of it. What is your voltage reference coming into it? 5 volts?

These are the kinds of problems that I love, cause it makes you think/diagnose the problem. Any one can be a parts swapper, but an educated individual would have the ability to narrow it down a little.

 

a bad ground can give you all kinds of problems

 

First off thank you guys for all the helpful suggestions..Just wanted to post a little follow up as I`ve tried a few of them:

>>>For me the purple text is a little hard to read, took me twice as long to read as it should have.<<<

I have done away with the purple text.

>>>How are the ground wires on the passenger side of the engine there should be 2 near the alternator,....There is also a ground on the back of the engine held on by a 18mm nut to the rear most head stud. What is the TPS reading when it is acting up?<<<

I hadn`t messed with those 2 particular ground wires before but today I undid them (The one wasn`t on very tight) and wire brushed the ends and contact points and tightened them back up...I`ll have to do any sort of electrical testing them on there another day but just cleaning them and tightening them had no effect..I replaced the other ground near the rear of the engine when I re-did my head gasket recently....The TPS is reading about 4.3 volts with the engine running at idle..That doesn`t change between running normally and when the check engine light pops on.

>>>Do one thing for me: disconnect all electrical connections from the alternator.......Have you checked into that little porcilen coil resistor lookin thingie over on the driver's side fender close to the firewall? This would have more to do with fuel pressure.....What is your voltage reference coming into it? 5 volts? ....These are the kinds of problems that I love, cause it makes you think/diagnose the problem.<<<

I`ll do this test when I get my good 1000 amp battery back from my brother..His van was having troubles starting in the cold weather and we switched batteries to eliminate that as a problem and now I just have this wimpy 550 battery in there....I`ll look into the thingie tomorrow...As mentioned voltage holds steady at around 4.3 with and without the TPS problem appearing.

>>> a bad ground can give you all kinds of problems <<<

Yes it can..I am going to run a ground wire off the coolant temperature sensor tomorrow also as this problem seems heat related..It seems to appear about the time a cooling fan would be coming on or a temperature sensor would be kicking in.

 

Coolant temperature sensor, the one in the thermostat housing, will cause this sort of situation.

Did you replace it with a new one or one from j/y?

If j/y item...get new one (DO NOT use the one from AutoZone...they are junk)
While you are at it, check for continuity in the wires. Fully remove them from the harness and visually inspect them if you must.

You need to clear your codes after replacing the sensor.
Disconnect the + lead and hold it to the - terminal for 5 sec. Then reattach to its home.
This will assure fully removal of any stored codes.

ALSO: Yours being a 94 won't have the porcelin resistor on the driver's inside fender.
That is a resistor for the fuel pump. IIRC this is a Renix-only item....where's that Renix Guru??? Is that last statement true?

 

I got one at the junkyard but it looked like it had been put on the Jeep the day before..Bright brass and the teflon tape was still pure white..I think whoever had the Jeep before it went to the j/y had replaced it hoping to cure whatever problem finally killed it but it turned out to be more serious than they thought..I get lots of practically "new" parts at the j/y because people try replacing various things (Sensors, starters, alternators,etc) hoping to fix their vehicles when in fact they have a more serious problem which ends with it being junked..If I am remembering correctly when the motor mount first broke on my Jeep I had a mechanic repair it as the bolts were sheared off and when I got it back I found the plug for the coolant sensor unplugged a day or two later and my seemingly heat related TPS code troubles started not long after ..Hmmm

 

If your TPS is reading 4.3V all the time that is part of your problem should be @.67-.80V(could be lower but most are in this range) at idle and just about 5.0V(4.6-4.9 is ok too) at wide open throttle.
My question now is how are you checking your TPS? With a meter or a scan tool? If a scan tool is reading that voltage all the time then I would check it at the TPS signal return wire and see what the reading is, if it is 4.3V then get a new TPS, if it is alot lower then you have a short to your PCM or internal PCM failure. On the TPS number 1 terminal VT/WT wire you should have @5V, on terminal 2 OR/DB you should have @.67-.80V, terminal 3 BK/LB is the sensor ground.

 

Yes Howler it is true. The last suggestion I have is the cam position sensor (not the crank but the cam) It is inside the distributor and that broken engine mount may have damaged it. Pull the dizzy cap and you will see it. It looks kinda half moonish. It takes the place of points and is activated by the distributors internal cam. It may be cracked or loose. Worth looking into and again the checking is free

 

Last year of that set up was 92 everything 93 and later uses a hall effect

 

Thanks, I thought that setup started in 96.

 

That is the reason most aftermarket performance ignition coils are listed as 93 and later, it will swap in place of a 91-92 distributor too, I have one from a 94 that I'm going to install with my stroker just to make it easier to replace the cam sensor.

 

Thanks guys I'll look into both of those possibilities today as it's suppose to be 51 and sunny here I thought about the distributor after all this first happened as the only thing which kept the motor from dropping was the bottom of the distributor came to rest on the motor mount and it took a few hard smacks on the way home but it all seemed pretty solidly built and looked in place so I left it be..But thinking of it now I guess the plastic up inside could have cracked..Does this seem like something that would only act up once the engine gets warmed up to a certain temp though?..The check engine light is really pretty predictable..If I leave my house and get right on the highway I can literally drive 100 miles or more and it will never come on until I pull off the highway and stop at a traffic light or slow down a lot then there it is..If I drive in the city in stop and go traffic it usually takes about 15 minutes..Again it all seems timed about when something heat related would kick in.
As far as the voltage I am using a good digital volt meter on the center hot and ground wires coming off the TPS..If I read the Haynes manual right I`m suppose to test it with the key in the run position (But the engine not running)..When I do that the voltage is as you mention .7 and then 4.x with the throttle wide open....When I said it was 4.3 volts that was with the motor actually running..I had hoped when something heat related kicked on it would change but it didn`t..But maybe whatever came on just sent a quick pulse that messed with something and wasn`t noticable on the meter