I've been having this weird issue for close to a year now, after driving and getting the jeep up to temp if I turn it off and leave for 5-30 minutes it will stumble when I turn it back on, after getting the revs up for a 5-10 seconds it goes back to normal.. The other potentially related symptom is when up to temp and sitting in idle at a stop light or in park, it will start to stumble after 30 seconds or so, it gets worse the longer it sits but goes back to normal as soon as I start driving again.

Any thoughts on the cause? 4.0 AW4 '99.

 

A pretty common problem is heat soaking. The engine basically boils away the fuel in the injectors/lines so it runs rough for a minute until normal fuel flow is restored

 

I believe that issue was limited to. 00-01s with the precats but I may be mistaken.

 

Interesting, is there anything that can be done about that, or any reason that it would show up as a relatively recent development? Actually I first noticed it at altitude, this developed when I moved from MA (sea level) to Utah (5000 ft)-- maybe that has something to do with it?

 

The lower air pressure could effect fuel vaporization. It typically shows up as cats begin to run hotter from age.

 

Aha, so I may be in need of a new cat? It appears to be the original cat so it may be time.. I do believe that my APN exhaust header has developed a leak at the manifold, that could be effecting underhood temps potentially?

 

Stumbling at idle turns out to be a bad distributor cap/rotor. The potential fuel boil off issue seems to be not as bad with a full tank which makes me wonder if it could be fuel pump related, check valve bad perhaps?