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Old 06-22-2010, 05:13 PM   #1
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97 TJ 4cyl cold idle/running issue

Less of a jeep question, and more of an overal engine question. When my jeep sits cold for any length of time, 10 minutes or 10 hours, it cranks and idles fine. But when I give it gas, it sputters and wants to die. Once you rev it up a few times, it runs like a top.
I thought it might be a fuel filter, but found out on this thing you have to replace the whole fuel pump!!! Wow.
Any thoughts or suggestions?

Thanks,

Ruprect.

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Old 06-22-2010, 05:32 PM   #2
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I am having that same problem... Its not to much of a big deal for me, but if it is an easy fix i would not bother doing so. Any thoughts on what this might be!

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Old 06-22-2010, 06:09 PM   #3
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(also try heat and your favorite penetrant from the back side).
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Old 06-22-2010, 06:38 PM   #4
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I usually start with cap rotor plugs before I go to fuel. are you sure there's not a fuel filter on the frame just foward of the rear drivers tire?
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Old 06-22-2010, 06:45 PM   #5
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I looked and there's nothing there, the fuel filter is in the tank and should never need to be replaced. And how would how no if you need a new cap?
Could it be the map sensor?
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Old 06-22-2010, 07:03 PM   #6
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don't jump ahead, start with the basics. how long since the last tune-up? how many miles? the cap if you pull if off will have what looks like corrision on the contact points. new caps have either alluminium or brass contacts nice and shiney. Pull one plug and see how it looks, how old are the plug wires? you can check resistance to see if one or more are bad. air cleaner? thats a good start right there, then on to the harder stuff.
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Old 06-22-2010, 07:16 PM   #7
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Did all that. Plus a tank full of Lucas fuel treatment. Got 198k on the clock.

Am I wrong to assume that if it was a fuel pump or filter, it would run crappy all the time? Because the stutter only happens when I first start it up and take off. It is honestly about 30-50 seconds into it running, whether it is still idling in the driveway or leaving the house about halfway through 1st gear. It stutters something fierce, but running out the clutch or just pushing the clutch in a revving the motor a couple time gets it through. Once it does it once, she runs perfect.
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Old 06-22-2010, 07:26 PM   #8
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Wide open throttle is when a weak pump would show up, but, check fuel rail pressure. maybe dirty injectors. throtle positioning sensor. those would be my next steps.
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Old 06-23-2010, 06:05 AM   #9
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having the same problem on my 97 4cyl w/102k. So far new plugs, wires, rotor & cap, air filter, and 3 or 4 bottles of fuel injector cleaner and it still hasn't fixed the problem. Took the throttle body off and thoroughly cleaned the junk out of it, which helped with the rough idle, and may have reduced the sputtering, but it's still there once in an while. I was thinking next of trying a new mopar tps. Any other ideas?
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Old 06-23-2010, 09:57 AM   #10
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I had the exact same problem on my 99 tj 2.5L and after some research on several forums I figured out it was the upstream O2 sensor. Apparently the heater circuit will go bad and tell the engine that it is warmed up prematurely and causes random sputtering until the engine gets up to temperature. You can test it by disconnecting the upstream O2 sensor plug and see if the problem goes away. I found an O2 sensor on ebay for 20 bucks or so, problem solved! Good luck!
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Old 06-23-2010, 02:06 PM   #11
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Glad I'm not the only one that had this problem. I'll try O2 and see if it works right after I find out why the damn thing won't turn over at all.

Thanks.
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Old 06-23-2010, 05:03 PM   #12
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Thanks sthomp.
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Old 06-23-2010, 05:20 PM   #13
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I had the exact same problem on my 99 tj 2.5L and after some research on several forums I figured out it was the upstream O2 sensor. Apparently the heater circuit will go bad and tell the engine that it is warmed up prematurely and causes random sputtering until the engine gets up to temperature. You can test it by disconnecting the upstream O2 sensor plug and see if the problem goes away. I found an O2 sensor on ebay for 20 bucks or so, problem solved! Good luck!
No check engine light? I thought about the various sensors but thought if they were bad the check engine light would come on.

Thanks for the info, I'll try it anyway in a few weeks and let you know!
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Old 06-25-2010, 11:04 PM   #14
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I followed Jerry B's advice and sprayed the airintake for the throttle body with throttle body cleaner. Having done all the electrical stuff, this worked for about 8 bucks.
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Old 06-26-2010, 08:21 AM   #15
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I followed Jerry B's advice and sprayed the airintake for the throttle body with throttle body cleaner. Having done all the electrical stuff, this worked for about 8 bucks.

So far this worked best for me too, but it isn't 100% fixed. I actually removed the throttle body, removed the sensors, and thoroughly cleaned everything with carb cleaner. That helped with the rough idle and every-once-in-a-while hesitation.

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