Topic: Hesitation on startup, perfect the rest of the day

[joey]

I've got an interesting issue with my 97 TJ.  about 99% of the time when I start it up in the morning it will rev up to about 1800 RPM and then try to stall.  If I don't do anything it will rev back up and go back and forth between idle and trying to stall. It will actually stall every once in a while.

I can back out of the driveway, but as soon as I get on the gas, it has no power and it takes quite a bit of skill to give it enough gas to get it moving while also fiddling with the clutch pedal.  After 10 seconds or so its perfect the rest of the day.

I am thinking that its the coolant temp sensor but I really don't have much to back that up with.  Any other suggestions?

Oh, I put a 4.0 TB on there about 6 months ago.  It was hesitating before I did the swap and it is still doing it after replacing the TB.  I cleaned all the passages and sensors on the TB when I had it off. 

[Jeffy]

The first thing to do is to check for 'Check Engine Light' codes.  Here's how: http://4bangerjp.com/forums/index.php?topic=3419.0

[aw12345]

Well its very well possible that it runs lean in open loop and once it switches to closed loop the ecm has some control and help make it run close to normal. Start with checking fuel pressure, next with a scanner check fuel trim. to me it either has a bad vacuum leak or a lack of fuel/bad fuel pump, most likely the latter

[99tj2.5l]

Maybe throttle position sensor i know my engine would rev up real high then almost stall at idle when it went.

It was really easy to replace too and im no mechanic...

[mgramann]

The hesitation could also be an ignition problem.  How are the cap, rotor, wires?  My jeep would act like that when it was humid and the spark would short out before making it to the plugs.  It would barely start then hesitate until it ran a bit and warmed up.  The 1800 right off the bat though has me stumped though...