hobhayward

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.

gyrator930

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

toasterknight

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

hobhayward

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?

toasterknight

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

hobhayward

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?

hobhayward

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?