Symptoms:
RPM drops irregular when slowing down
idles poorly +/-50RPM or so but bounces in that range, rarely consistent.


IAC and TPS are new. Battery may be old and sketchy though. Grounds appear in good shape.
I get 2 readings from the female connector at the TPS: 5.16 (driver side) 4.34 (middle) and 0 for the left obvi.

 

Here's TPS tests for a 97-01 XJ.


I use safety pins as back probes. They work good.

 

Hi CCKen, yes thank you.

Ground - check
5 volt - check
TPS signal - .97 and 4.00

The tps was replaced a few months ago for the same symptoms that never went away. Now, this isn't MOPAR TPS.. it's whatever autozone sells (I don't recall brand).

Is it the TPS causing my p0122? I didn't have the code at time of the first post but after poking and prodding the code came back (it had popped up a while back but I did some stuff and cleared the code and it didn't show up until yesterday).

 

well, the P0122 has gone away on its own but the idle issues remain... I replaced IAC a few months ago btw

 

Did you remove and clean the TB when you replaced the IAC?


The IAC pintle bore in the TB gets gummed up.

 

cleaned throttle body probably 4 times last fall when the issue started. replaced MAF, IAC, TPS, plugs ...

Interestingly, the voltage isn't the same from directly plugged into the TPS vs backplugging it. I"ve had the throttle stick at the sensor and I wiggled the wiring harness to the TPS and it started idling perfectly... I just don't know how to fix the harness. I'm pretty sure it's a bad ground wire there bc it's a little kinked directly at the base of the harness. I'm checking with the local chop shop to see if i can get one otherwise I've got no clue..

 

im thinking the mid should go from 0v to 5v appx with throttle movement thru the full range. its like a resistor with 5v one end and ground on the other the mid is a slider that reads 0 to 5v to show position to the computer. like a volume control on an old radio.

 

I think you have found your problem. The repair is simple in concept, but a pain to actually do. You need to replace that ground wire. You cut out the old, and splice in the new. Easier said than done! But it's just tedious labor - there's nothing complicated about it.

Try this: take a few pics of your harness, especially that kinked spot, and post them up here for a look-see.

Ken, have you got a diagram that shows the ground point for that sensor? I'm thinking a good ground cleaning won't hurt, even though the wiggling changing the idle points to some flaky wiring.

 

The ground is inside the PCM. All sensors on the ground network are grounded inside the PCM.


Wiggling the harness and it runs better means you need to tear apart the harness to find the fault. It's a short harness from the TPS to the plastic fuel injector wiring harness manifold (which the TPS, CPS, MAP, and IAC go thru). Unwrap the harness and look. You may have to open the plastic manifold to look-see.


Also, look at the wiring harness where it exits the plastic manifold. Occasionally the end of the fuel rail will penetrate the loom and hit the wires within.



.

 

Ken, is that the head-to-firewall braided ground wire I see in the background there? Frayed and broken?

If so, you need to replace it with one of those nice 4 gauge replacement cables that some folks sell! Nah, go big or go home! Make it 00 welding cable!


Okay, on a serious note, yes, the wiggle test means it's just time to get into that harness. Be glad it's so repeatable! At least you know where the problem is!

 

Not my engine bay. Stole the pics.