A few questions re 98 XJ

I had some issues lately with my xj idling high, low and cutting out while driving. I didn't think this was an overall electrical Problem as just he tac dropped when the engine stalled. It wouldn't normally die, just the RPM's would tank momentarily.

It was suggested that I replace the throttle position sensor and I did. This seemed to fix most of the problem. However it still runs at a higher that normal idle (around 1300 RPM) and occasionally cuts out. Just not a severe as before.

I bought the $60 TPS rather than the more expensive one. was this a mistake. Could it still be the TPS even though it is new?

Next question. I use this jeep as a daily driver and do very minimal offroading (mostly during hunting season). I'm getting a little tire rub and some of it is on the plastic skirt in the wheel wells. Do you all ever just rip those out? Or should I keep them and modify them?

I am considering putting a set of Bushwacker flairs on it in a few months anyway.

You can test the TPS. If it is within specifications, suspect that the Idle Air Controller is faulty. If the stalling continues or gets worse, suspect the Crankshaft Position Sensor is faulty.

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. The PCM receives an input signal voltage from the TPS. It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. This will vary in an approximate range of from .25 volts at minimum throttle opening (idle), to 4.8 volts at WOT wide open throttle.


Cheap parts are cheap for a reason. Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.

Tim,
Thanks much for the sage advice. I really should have known better than choosing the cheapest TPS out there.

Quick update on my idling issue. I replaced the TPS with an new sensor genuine jeep sensor as suggest by Tim. It immediately started working correctly and I haven't had an issue since.

lesson learned. Thanks again.

Thanks for the follow-up, glad to hear it was a simple fix.

FYI, I carry a spare genuine Jeep Crankshaft Position Sensor in all 3 of my XJ's. A failing CPS often gives little to no warning symptoms, and can leave you stranded.

Mine gave me plenty of warning.
Just took me 2 weeks to be sure that it was the CPS.
And even then I was not 100% sure. Just stalled when she reached operating temperature.
In the beginning she would start right back up. Sometimes stall again but start again. Sometimes I would get to where I was going. All local short trips though.
No CEL or pending codes. No other stuff I read about associated with a bad CPS.
Just thermal failure IMO. Even trying to do the resistance test was telling me it was bad.
Which made sense cause it only stalled when hot.
New Mopar CPS and was good to go.
In anticipation that at some point Mopar CPS's won't be available anymore bought one for "stock". LOL.

Meant to say when doing the resistance test was telling me it was good.
Wish I could edit here.

Mine went out in a single day. Drove cross Texas to Big Bend, then rattled the XJ around 15 miles down the 4by roads to a camp site. Camped, then drove back out to the Chisos Basin the next day. Then and only then I started having some cutouts that felt like I had stalled it even though I wasn't shifting (AX15). This happened 2 or 3 times up the mountain. Finished the day and were heading back out and on the hour long drive out it happened a half dozen times more. Then just as we were hitting cell coverage thank goodness it finally died and couldn't be restarted.



In retrospect I bet if I had let her cool I could have gotten her to Alpine but instead we were towed the 1h45m the rest of the way to a garage. Engine had thrown a code but I didn't have a code reader on me.



Took two days and me FedExing the CPS from Austin because the local garage couldn't locate parts (not blaming him, it was a very small shop) to get her running again.


Long story short, I think the CPS was on its way out and it got rattled just out of spec. Now I carry a spare and the extensions to swap it out if need be. But it can die in a hurry.

After 17 years of XJ ownership, the two spares I always carry are a CPS and a TPS, the two sensors that seem to die at a moments notice and leave you stranded..
Make sure to carry enough extensions and the right size socket to pull the CPS and the correct torx wrench to replace the TPS.

I agree whats been said above.
First i replace any an all sensors with genuine Mopar parts.
Yeah they're more costly but they work.

Far as the CPS in my experience they can fail intermittently usually when hot like on my old '94 xj or abruptly fail all of a sudden dead in the water without warning like on my current '2k xj.

My 2K xy's original OEM CPS made it to some 250,000+ miles before failing.

OP, far as erratic idle rpm two things come to mind to check first if the Mopar TPS doesn't work out.
Vacuum leak or the IAC valve.

xjnp242 said:

I agree whats been said above.

Far as the CPS in my experience they can fail intermittently usually when hot like on my old '94 xj or abruptly fail all of a sudden dead in the water without warning like on my current '2k xj.

Click to expand...

Both of the CPSs that have gone bad in my XJs have failed when hot. Cooling them every couple of miles with cold water has enable me to get home or camp and yes, both were genuine Mopar.

My 2001 CPS could not be seen when stock. When the engine was out, I rearranged the wires and hoses to provide a straight shot at it, to ease field replacement.

lazyxj said:

Both of the CPSs that have gone bad in my XJs have failed when hot. Cooling them every couple of miles with cold water has enable me to get home or camp and yes, both were genuine Mopar.

My 2001 CPS could not be seen when stock. When the engine was out, I rearranged the wires and hoses to provide a straight shot at it, to ease field replacement.

Click to expand...

Yeah, with my '94 CPS failure, usually happened after parking a hot engine for 20 minutes. Probably a heat soak issue.
Letting the engine cool off another 20 or so minutes worked to get going again.

With my current 2000 CPS failure a whole different story.
I stored it in my pole barn a few years ago for a couple of Winter months.
Worked fine when parking it but a couple months later when i went to start it...crank crank no go. Yep turned out to be the CPS.