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Old 12-01-2010, 10:09 AM   #1
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TJ starts right up but wont stay running

I have a 1998 TJ, 4L with 110K on it. This has been driven hard on the trail.
It starts right up cold but after a few minutes pukes out, then wont stay running long if I'm able to restart it.
I did put a fuel pump in it last year and only drove maybe 2K miles.
I know the quality of the aftermarket parts can suck but fuel pump shouldnt be out already.
Any other thoughts?
CPS, throttle body, or ?
Appreciate any help. Thanks.

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Old 12-01-2010, 10:21 AM   #2
Knows a couple things...

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If it runs ok when you step down on the accelerator pedal but won't idle once you take your foot off the accelerator pedal, likely your IAC (idle air controller) is simpy dirty and needs cleaning with throttle body cleaner which comes in an aerosol can. The IAC is what provides all of the engine's air at idle when you are not stepping down on the accelerator pedal.

After removing the air intake tube from the throttle body, start the engine and start spraying the throttle body cleaner down into the throttle body. Aim some of the spray into the little slot above the throttle body's butterfly valve plate which is the IAC's air intake. That will get the TB cleaner spray into the IAC area though it only sucks air (cleaner) into it at idle so you'll have to try to keep the rpms as close to idle as possible with the throttle lever. That may clean the IAC well enough to fix it. If not, remove the IAC (it's only held on with a couple small torx screws) and clean its plunger with the point on the end with a toothbrush and the TB cleaner. Be gentle with the plunger, don't twist or push-pull on it. When the IAC is clean, clean the oriface in the TB that its plunger fits into too. Use the TB cleaner and a small brush like a baby bottle nipple brush.

This is what the IAC looks like...
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Old 12-14-2010, 09:32 PM   #3
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Jerry, you just saved me a bunch of money! ive been having a rough idle problem; it would idle smoothly for a couple seconds, but then it will stumble. the tachometer would drop when it stumbled, then it would recover and idle smoothly again for a short time.

i cleaned my throttle body with cleaner spray... it didnt help, but it sure looks shiny now. i read this and thought cleaning my IAC might help, so i pulled it out and it was dirty as sin. cleaned it thoroughly (and the housing) and reinstalled it, but the rough idle still persisted. i was fed up and considering taking it to a real mechanic...

but i got back on here and read through a couple more threads until i found your reply on this thread. i sprayed cleaner into the IAC housing while idling, and it cured my rough idle problem. thanks a bunch!

here is what my IAC looked like before i cleaned it:
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Old 12-15-2010, 12:43 PM   #4
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Could also be a coolant temp sensor. When cold, your engine gets high amounts of fuel to warm up, basically like a choke on a carb. As the coolant temp increases it backs off the amount of fuel needed. If you're engine is getting warm and the coolant temp sensor is telling the pcm it's still cold then it is basically flooding the engine with fuel causing it to stumble and quit. You say it will start cold but after a few minutes quits and you have a hard time restarting after the engine is warm, it sounds like maybe a coolant temp sensor.
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