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2K IDLE - Odd Shifting - TPS? (I know.. I know)


NAXJA Forum User
Hey yall!

1998 Jeep XJ
Automatic Transmission
2WD No Transfer case
172K miles

I know.. another damn TPS high idle post. I am pulling whats left of my hair out.

Jeep has been running fine. Florida Jeep born and raised, not a lick of rust. On my way home from work Monday we were having some serious rain - randomly the XJ down shifted and when pressing on the gas peddle the RPM's would continue to rev up 3K+ and the jeep would not shift into higher gear but would continue to move forward. I immediately thought "Damn my transmission just blew up" but I could get it to shift if I rev high enough and quickly let go of the gas. CEL is on - pointed to the IAT (I replaced IAT about 4 weeks prior because of a random CEL) I purchased a MOPAR Sensor. IAT OHm was perfectly fine. I also installed the old one back to test.

Worth noting my MAF, IAC, TPS are all new MOPAR. Most only being about 2 years old.

Was able to limp her home around 45-50MPH to keep the RPM's right above 2K (Didn't want to rev the piss out of it the rest of the way home)

Put in park the RPM's stayed at 2K. When I drop to D the RPM's do lower a little bit but does not want to shift. Anytime I start her up she creeps right back up to 2K and stays there. Still does not want to shift but goes into reverse perfectly fine.

I checked the shift linkage on the transmission and on the TB. All looks fine.

So I did some research and thanks to the awesome people on this forum in the past it seems to be related to possibly the TPS. I changed the TPS about 2 years ago - I also changed the Clock Spring a year ago.

Why do I think it might be the TPS? Well I back probed the TPS sensor, while connected to the jeep and off - I am getting my 5V power, but I am also getting 5.15V at the sensor - even with it off of the sensor. I was looking for dead spots but the damn thing is already at 5V and increases to about 5.5 with the TB fully open. It should be around .2 or .4.

So... more research:

1. Unplugged horn relay and fuse
2. Unplugged both air bag fuses
3. Unplugged TCM
4. Unplugged all TB sensors
5. Unplugged Clock spring harness and airbag

I am still getting 5V at the sensor wire. The ground wire is registering 0.08V but I am not 100% sure if that's just my multi meter or if that's a problem.

I inspected the grounds and they appear to be fine.

I come to yall to show me the way. I'd be lost without yall. Any help at all would be most appreciated. Thank you!
Sounds like a bad TPS to me. Measuring the signal wire unplugged does tell you anything, btw. Gotta backprobe it while plugged in.

Thanks Lawsoncl!

Yea I did both actually. I back probed it while it was plugged in and in the TB. Still getting 4.98-5.15V.

Today after cleaning everything up it appears I got the idle under control. Does not appear to be reving to 2K. First shift feels okay, second feels like the jeep wants to stall and the 3rd is either to quick or a rough shift.

Not really sure what in the world is going on.