Electronics problem? Multiple intermittant issues

'96 stock XJ 4.0 HO Sport auto 4wd 303,000 miles
Top End Rebuild @ 200K miles
"Another" transmission at 200,000 miles
TPS and IAC have less than 25K miles on them
Coolant Temp Sensor and Temp sender have about 40K miles on them
Plugs and Wires have less than 15K miles on them
Alternator has less than 25K miles on it
Cap/rotor - unknown age - 45K miles + at least


I was pulling a hill a couple of days ago and several times it felt like I was losing power for a brief second. A couple of miles later I pulled a bigger hill. The tranny shifted multiple times between 4th and 3rd gears while going 65mph when it normally doesn't shift at all. It would go back into third for just a second then right back to fourth and back to third again over and over. My torque converter is stuck unlocked and has been for a long time.

I stopped at a store and when I pulled out onto the highway it hesitated halfway through first gear. I drove another sixteen miles after that, hills included and it ran perfectly. The next day I made two long trips totaling around one hundred miles and it ran perfectly.

Today I drove eight miles to the store with no apparent issues other than it seemed to hold through the gears a little longer than it should. When I put it in Park the RPMs went up to over 1500. I put it back in reverse and the RPM's dropped to normal and went back up again when I put it in Park.

I thought maybe I had another vacuum leak. I did my shopping and let the motor cool down. When I started it back the RPMs went up to almost 1900 then went down to around 1100 and would fluctuate by a few hundred in either direction but the motor ran smoothly. While that was happening I noticed that my Low Washer warning light which always stays on was going on and off which led me to believe I might be having a computer issue. I turned it back off, had a smoke and fired it back up again. Everything was back to normal. I drove several miles on the highway and in town and made several stops with no more problems.

I know you mentioned you replaced the TPS and IAC. These are two things that I would think of right away. Maybe try testing the MAP sensor vacuum, their is a little hose underneath it on the throttle body so you can record vacuum and voltage and whatnot for that sensor. 25k seems to early to have a TPS malfunction or a dirty IAC. I'm guessing you have thoroughly cleaned the throttle body. I once reassembled my 4.0 throttle body after cleaning it. I had somehow got some moisture and cleaner in the TPS and when I plugged it all back in and fired the engine, it had the same symptoms you described. I tested the middle wire on the TPS terminal while this problem was occurring, and it started off reading 1.2 volts at idle with key on engine off. and when I opened up the throttle, it had spikes/drops/dead spots in the voltage, and it only ended up at 3.7 volts at wide open throttle. When normally functioning, it starts at .7 volts and rises smoothly to 3.9 to 4 volts. I took the throttle body off as the torx bolts were seized so that's why I took the whole TB off and also why moisture got into it when cleaning it cuz I couldn't separate it. I then placed the TB over a heater vent for 3 hours and re installed it and it passed the voltage test and then turned it on with problem fixed. Those are the only things I know of to contribute to a sporadic up and down idle that doesn't also feature a noted stalling aspect.

How you described it fixing itself is why I brought up my story with the moisture and it fixing itself by drying the TB and all its attached sensors. made me think of the moisture problem. I don't know if you wheel your jeep in deep water/mud but who the hell knows how moisture finds its way in things sometimes.

I appreciate the response!

I don't know what the deal was but I have driven the Jeep for another week now with no issues at all.

It acted up once before after a period of heavy rain and then the problem mysteriously vanished. Engine stumbled and then stalled out, then ran perfectly after I started it back. Perhaps the TPS is getting moist at times. I do live in a humid area. Something is getting moist, shorting out, something. I still find it curious that my "Low Washer" light was going on and off. Something isn't right there.

I'm still rolling though. :scottm:

One of the first things I do in this situation is to recheck my TV cable adjustment. Easy to do and reduces the possibility of confusing a mechanical issue with a sensor or electrical issue.

Next thing I do is to reboot the computer and drive it for awhile. My 96 has some reprogramming as you drive glitches that sometimes manifest over days and weeks. These issues may disappear with a reboot.

Kind of sounds like you have a TPS issue. The trans TCU and PCM share the same TPS. I saved my old TPS when I swapped in a new one. A quick check is to swap in the old one and see what happens.

The lower the voltage the less the chance that moisture is going to play a roll. Though a wet TPS is a known trouble point.

Windshield washer fluid and coolant passes low voltage better than water alone does. Radiator leaks or windshield washer splashing out the cap can cause issues quicker than water alone will.

One thing that is often forgotten is that many sensors share a common power source and when one sensor shorts (or partially shorts) out the major issues may show up as something totally unrelated to the actual cause. Low sensor input voltage (in general) can screw up numerous sensor output readings.

The last time I was almost certain my TPS was screwing up it turned out to be a front O2 sensor. That O2 sensor never threw a code until it completely died, it was acting up for months.

I doubt anybody on the planet knows how the sensors interact completely. Garbage in garbage out, I doubt the programmers anticipated every possible scenario.

fishinpolejoe said:

I appreciate the response!

I don't know what the deal was but I have driven the Jeep for another week now with no issues at all.

It acted up once before after a period of heavy rain and then the problem mysteriously vanished. Engine stumbled and then stalled out, then ran perfectly after I started it back. Perhaps the TPS is getting moist at times. I do live in a humid area. Something is getting moist, shorting out, something. I still find it curious that my "Low Washer" light was going on and off. Something isn't right there.

I'm still rolling though. :scottm:

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Somebody else with a 92 has similar issues, I think his started acting right after a car wash.

Green Mesa XJ said:

Somebody else with a 92 has similar issues, I think his started acting right after a car wash.

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Don't folks usually say check the fuses in the passenger kick panel for corrosion or at least moisture if there are weird electrical issues after rain, stream crossings and the like?

dan1977p said:

Don't folks usually say check the fuses in the passenger kick panel for corrosion or at least moisture if there are weird electrical issues after rain, stream crossings and the like?

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Considering that if the door isn't sealed up tight, rain from road cruising splashing, and deep water getting in through the door and the panel being right on the floor, and cool moist air sinks...seems pretty logical that it would pose a threat. I have had a few fuses in the kick panel randomly blow repeatedly, and spraying contact cleaner and putting a heater in front of it for a while solved the issue. I have also found sensor plugs/connectors not locked in all the way, causing some sporadic issues. I have electrical tape wrapped on all m wiring know, and even over the connectors so moisture doesn't get in and I have had much better luck out in the mud lately after doing that. All I know is I don't attempt to clean the engine area anymore with anything except a wet rag and wiping everything. I have had electrical problems every time I degreased and rinsed the engine bay even with bags taped over alternator, sensors, PCM. Let's see Jeep design an XJ water crossing limited model with waterproof electronics haha

dan1977p said:

Don't folks usually say check the fuses in the passenger kick panel for corrosion or at least moisture if there are weird electrical issues after rain, stream crossings and the like?

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Every XJ i've owned has had a leaky windshield at some point. Used to replaced the windshield primarily because of rocks cracking them, now I'm more likely to call for a replacement to seal it up again.

One has a drivers door that always leaks around the top seal, like in a car wash or very heavy rain. Used a few tricks a buddy who does body work to bend it back a little, changed seals to the 97 up, a little better now. Used to think it was because it was hit on the passengers side and repaired before we got it, but the guy who does body work didn't have a nice thing to say about Cherokee doors so maybe it was always a issue.

Green Mesa XJ said:

Every XJ i've owned has had a leaky windshield at some point. Used to replaced the windshield primarily because of rocks cracking them, now I'm more likely to call for a replacement to seal it up again.

One has a drivers door that always leaks around the top seal, like in a car wash or very heavy rain. Used a few tricks a buddy who does body work to bend it back a little, changed seals to the 97 up, a little better now. Used to think it was because it was hit on the passengers side and repaired before we got it, but the guy who does body work didn't have a nice thing to say about Cherokee doors so maybe it was always a issue.

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My windshield leaks and my driver door does too. I try to park mine with the nose uphill when it rains which minimizes the leaking. I've replaced my carpet with vinyl flooring to prevent moisture being held against the floorboard.

I had a good look at my kick panel fuse box with a good flashlight. All the contacts looked surprisingly bright and clean in the empty spots.

I never wash under the hood and we haven't even had a good rain in a while. I rarely go more than sidewall deep in mud or water either. This is about as off road as it gets for me:

The only fuse panel i have trouble with is because of the clutch master cylinder leaking. Probably combined with leaking windshield.

The others seem to dry out well enough. Right now the windshields aren't leaking but there's always another place like the movable vent glass.


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Green Mesa XJ said:

One has a drivers door that always leaks around the top seal, like in a car wash or very heavy rain. Used a few tricks a buddy who does body work to bend it back a little, changed seals to the 97 up, a little better now.

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My 99 leaks like a sieve... The hinges are shot, so hopefully when I rebuild those it'll tighten up.