Weird idle prob

Usually when I stop at a stop light or something the idle of the jeep seems to be around 800 or so rpms. Lately sometimes it idles up past those rpms around 1000 or more and is hard to stop but once stopped sometimes it goes away. Sometimes it doesn't stop high idling and I have a hell of a time stopping the jeep, but luckily this only happened in front of a house twice. One time while idling sitting in front of a friends house the rpms started creeping up to around 1000, so I threw in neutral and then it jumped much higher and then I threw in park and they stayed and wouldn't go down, so I shut the jeep off. They stayed high when I turned it back on. What in the hell is this tps?? I have a practically brand new one on there with a spliced in ground wire so it reads correct volts. Should I recheck the voltage? ---------kyle

You complain you have a problem at idle. There is a TSB to fix the idle air controller. Take it to a dealer mechanic who understands the renix XJs. Have the throttle body cleaned, as part of the service they will check all engine sensors and recal the TPS if necessary.

I´ve had intermittant high idle on a couple of XJ´s, on various occasions. Turned out to be a cut vacume line, to the vacume resivoir on one and loose intake bolts, on two other occasions (would occasionally idle over 1000). Another was a fried wire (rubbing the exhaust manifold) to the temperature sender, low left of the block (never idled more than around 700-800 by my tach).
Vacume problems also seemed, to make the motor idle somewhat rough. The RPM´s would vary at idle and occasionally run at a seriously high idle. Flunked the emission test for high HC on that one.
The idle is beginning to fluctuate on my (new to me) 88 lately, I plan on cleaning the throttle body, changeing the intake /exhaust gasket and adjsuting the TPS. I overheated mine a bit, the other day, doing a coolant change and the idle went way up (for awhile), figure the intake expanded and/or moved a touch or the bolts are loose.

Great info,

I am having the same problem with the idle on my new to me 87XJ. It seems to idle fine when first started, but as the vehicle warms up the idle wants to climb.

Copperhead

Same deal on my 90, I cant find a vacuum leak, But once it warms up it like to idle at 1300. Its the TPS im sure.

The C101 has given me these symptoms. It's a real bear to clean up due to the very sticky grease they used on it at the factory.

idle gremlins

I've been getting this idle gremlin too. I have been doing a bit of research to solve it. Sounds as though its a vacume leak. As a test I was told to run a propane torch (unlit - DOH-) over the lines/junctions and the INTAKE. We have an aluminum intake as being that, aluminium expands faster than the cast head its attached to creating a problematic area.
Anyway... the propane is supposed to increase engine RPM as it finds the vacum leak(s) as you pass the propane over the area it will be sucked in and either smooth out the rough idle or increase RPM noticably. I havn't actually tryed this but seem to make sense.
Any of you tryed yet? I would think a carb cleaner or even brake clean would work well too.. thats pretty hi octane stuff and would also be sucked into any vacum leak....
Once my engine warms up it seems to mellow out and behave though so I suspect the intake bolts are loose. When it warms up I'll get in there and retorque them. Best of luck to the rest of you, stay in touch and let us know how you killed your gremlin.