rough idle after long trips

Hot idle problem, 94, 4 litre
Does anyone have any ideas on idle problem with my 94 xj, 4 litre sports.
The Jeep is stock with only very low mileage, about 60K miles and I've had it since new.
Starts and runs fine, performs real well, but after several hours at highway speed it starts missing at idle and has a slight hesitation just off idle. The temp gauge is still at normal so it's not running hot.
This doesn't happen running around town only after several hours on the highway, like annual vacation time. (Iv'e just returned from a 600 mile trip)
It has now settled down after running around town for 2 days.
Unfortunatly local dealer is also a Toyota dealer and Jeep runs a long way down on his list so they are of little use.
Any ideas?, Regards aussie Paul.

it would be difficult to say for sure. but i have had 2 similar complaints. 1 left undiagnosed and the other after much driving and a few data recordings with a co-pilot. showed that an injector was leaking only after long drives. why? i don't know. i replaced all the injectors and the condition did not reoccur. does it puff black smoke when acting up? a few other possibilities are crank sensor after heating up.does it have an egr valve? i know mine doesn't but i don't know if an aussie model is a different spec. i had a caravan the other day that would only stall after long trips. the pin hole for vacuum to the egr had corroded over just enough to only allow vacuum in after long drives and not back out when stopping.until it sat for about 20 mins. fuel delivery issues fuel pump overheating.weak coil. i had a dakota once that acted up only after 1.0 hrs of driving the cat. was stopping up. but it wouldn't run at all.
there's probably other stuff i've worked on that a couple brews might jog my memory of. hope this might help a little. oh yeah 02 sensors can do it to but they are normally just the messenger.

Thanks for the suggestions. The Aussie versions don't have a EGR set up on them, at least my '94 doesn't anyway, not too sure about the later ones.
You mention two things I have had doubts about. 1 The leaking injector. I tested the leak down rate a while back and they only just passed the factory test, I tested all of them in the circuit though, so don't know if may be one is playing up, it's a possibility though.
The 2 nd thing is the crank sensor, from what I've read, these are a problem and I have thought I should have a spare one anyway, it can be a long way from a dealer out here if your break down.

Anyway once again, thanks for your help, let me know if you think of anything else.
Regards, Paul

I´d be tempted, to coast into a rest stop and pull a few plugs. Check the color.
My old 87 after 80,000 miles or so, seemed to do better with a slightly thicker oil. Can´t say why, just seemed to help smooth things out a bit.

Clean the throttle body...Remove the TPS and ISM...then use a good throttle body cleaner....Best to remove the TB from the intake. Bet this will solve the idle problem...also if damage the gasket to the intake replace it.

I'm definately not an expert, but maybe a defunct IAT sensor? This sensor reads temperatures in the intake manifold, and adjusts the timing accordingly. Cooler temp = timing advance, Hotter temp = timing retard. Just a thought.

Greg