I have a 93 XJ With a 4.0. The jeep use to belong to the state police department, and has 219,000 miles but don't look or run like it. Everything works on the vehicle, no smoke when running and no leaks. Everything motor wise is stock to my knowledge. Now to the question. When the jeep sits for a day, it starts fine but with a rough idle for 30-45 secs. If I let it idle it will die and then I have to hold it to the floor to get it to start. If I feather the pedal for the 30-45 secs and get past the rough idle it runs fine, and continues to idle correctly for every start thru out the day.

 

check the fuel pressure

 

checked the fuel pressure and it reads 32-34lbs while cranking the motor and during the rough idle. once the idle levels out the pressure stays the same. I pinched the vacuum lines to check them. unhooked and check the return line and that was fine. I changed the fuel filter, since it was cheap and to eliminate one thing from the problem. any other ideas? thanks

 

key on key off method check for codes even if lights not on

 

Rough idle clearing out after a while especially (after the car has sat for a while) could point to a leaking injector. The rough idle is the engine clearing the excess fuel.

 

very possible

 

That is my first thought as well.

As you have a gauge, hook it up and watch it after you turn the engine off. Watch how the pressure holds up. Does it stay about the same for the first 10 minutes, or does it drop quickly.....if so, give details about the exact pressure drop.

 

Did the key on / key off method and no flashing from the check engine light, stays on for a sec then shuts off. I did the 30 min leak down test. Idles at 32psi, shut off drops to 30 psi. 1min 34psi, 2min 36psi, 3min 37psi, 4-12min holds at 38psi, 13min 37psi, 15min 36psi, 19min 35psi, 20min 34psi, 25min 33psi, 28min 32psi, 29min 31psi, 30min 30psi. Hope this helps. Tried to get detailed with out dragging it out. Thanks guys