The long trip heat soaked the engine and probably extended the crack. It takes about an hour to an hour and a half at speed for all the working parts to reach their max working temp. My buddy drives the big rigs and he said each morning he gets on the road, the first hour is the most critical. If nothing breaks by then, it's probably good for the rest of the day.

 

I'm going to get something to try to patch that crack tomorrow morning and see if that helps at all.

 

So, the solution to my problem was, well, interesting. I've spent so long tearing things apart, cleaning them, putting them back in, all with no luck. Cleaned the IAC and throttle body, checked my TPS, checked any vacuum lines I could see. Nothing. So I disconnected my throttle cable, started it up, boom, no more high idle. Thought maybe it was a bad connection there somewhere or in the cable.

But, after four hours of work the other day, I found that the wiring harness to the module for the damn cd changer that the PO had put in had frayed and must have disconnected when I hit some potholes on the interstate the first night it started doing this. The damn harness was blocking a section of the accelerator pedal and wasn't letting it release fully. The only way I could explain the problem to people was that it sounded like the accelerator pedal was stuck...and it was. I just fixed all of this with two zip ties. Running like a top again, just need to change my oil and do a tune up lol.

 

This is going to sound really really stupid, and I'm certain most will roll their eyes and mumble to themselves "this guy is a *******". I had a similiar issue with my 01 GC Limited 4.7L. For nearly two weeks it would start and idle at high rpm until "warmed up", then level off. I went thru the process of elimination, cleaned throttle body/housing, vac, plugs and wires. Then I did an oil change... Noticed I was 2 1/2 qts shy when draining. I scratched my head wondering where the hell those 2 1/2 qts of oil went, shrugged it off then finished the oil change. After all was said and done, I started up the jeep and to my surprise.. no high rpm! Now between me and the dog that watched me do the oil change, I'm almost convinced it was all due to being down 2 1/2 qts of oil. But that's just me (and Rover).

 

Thanks for your comment Columbus. I was really worried as I just changed the piston head on my 00 XJ and after everything was put back together it was starting at high rpm (around 3k). My first thought was "I really f'ed this time". After I read your post I realized I did not put even a qt in the motor. I filled up and voila... Running smooth like a baby's cheek. So, yor are not the only *******

 

Rueter, doesn't it just burn your ***** when it turns out to be something stupid like your throttle actually sticking? This is not something you would normally check.

 

I have had the same problem and have replace all those parts awhile ago and it seemed to fixed the problem. Now a few months later it started doing the same thing again. I checked the bolts on the manifold and they where about a quarter turn loose....did nothing to the problem. Wiggled wires...nothing. Unplugged the connectors to the modules around the intake body and then wiggled and pushed on the cable over on the computer that sits on the firewall. Low and behold it stopped fast idle.
Conclusion a minor corrosion on a connector or loose or the known loose connector connections on the computer. Who knows....will see what happens.
PS: Have had a none starting problem on another jeep and replacing the computer because of cracks caused by the cables pulling on the board over time.