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#965821 - 08/15/07 12:40 AM 4.0 jeep cherokee rough idle
rt_ponder Offline


Registered: 09/11/06
Posts: 64
Loc: over the edge....of the Sierra...
Hey folks!! Got a 96 4.0 w/160k on it. Does anybody know what can cause a rough idle.....put new plugs,cap rotor. Runs great, powers good,still get the same mpg. Anyone....anyone?

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#965822 - 08/15/07 01:29 AM Re: 4.0 jeep cherokee rough idle [Re: rt_ponder]
Eddie Offline


Registered: 12/07/03
Posts: 8492
Loc: Florida, Cape Coral
You did not mention ignition wires. Try some TECH RON CONCENTRATE FUEL SYSTEM CLEANER. WalMarts for ~ $7. Don't brother with the injector cleaner but, use the system cleaner which is a stronger formula.
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#965823 - 08/15/07 05:44 AM Re: 4.0 jeep cherokee rough idle [Re: Eddie]
HardbodyLoyalist Offline


Registered: 08/06/04
Posts: 707
Loc: Lower Alabama
Check the idle air control (IAC) valve.

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#965824 - 08/15/07 05:52 AM Re: 4.0 jeep cherokee rough idle [Re: HardbodyLoyalist]
punisher Offline


Registered: 09/11/04
Posts: 2349
Loc: snowblind in TX
First rule on rough idles, ck for vac leaks. It's free, and usually the culprit.

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#965825 - 08/15/07 07:13 PM Re: 4.0 jeep cherokee rough idle [Re: punisher]
gomes512 Offline


Registered: 07/02/07
Posts: 666
Loc: Chicago, IL
My experience with the 4.0 is that rough idle is usually caused by vacuum leak as mentioned above already. Just take a fine powder and fluff it when the motor is running by lines and see if any is being drawn towards a section of line. Or you can mist wd-40 and get the same effect.

IAC as mentioned above also, will cause rough idle and fluctuating rpm's when in park. Another culprit is a bad Throttle Position Sensor (it is located right next to the IAC in the throttle body). When it goes bad it will think the throttle plate is either to closed or to open when in reality it's fine.

I usually change out the above two sensors together as bad idle annoys the living ---- out of me. After that I'll go and buy the Chevron fuel cleaner as mentioned and run that. I also buy a can of Mopar combustion chamber cleaner and shoot that down the throttle body (has helped my idle).

If you really feel the motor shaking when idling then that is a sign of deteriorated motor mounts. After replacing mine this summer... what a world of difference.

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#965826 - 08/15/07 07:25 PM Re: 4.0 jeep cherokee rough idle [Re: gomes512]
rt_ponder Offline


Registered: 09/11/06
Posts: 64
Loc: over the edge....of the Sierra...
All youz guys, Thanks for the input. Back to first post....plug wires replaced w/ tune-up,have already "treated" intake w/chemicals. Mounts are fine,checked that too. To clarify.....idle is not "rough", more of a sputter....gomes512, good point on TPS,thats my next test....maybe a crank position sensor also? I'm gonna finish my coffee and get to it....willpost findings later....

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#965827 - 08/15/07 09:31 PM Re: 4.0 jeep cherokee rough idle [Re: rt_ponder]
dwendt44 Offline


Registered: 05/17/06
Posts: 3637
Loc: Central Wisconsin
Clean the throttle body helps sometimes.
Did on a GM V-6.
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Too large of a gas tank,
or too loud of a horn,
or too bright headlights.

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#965828 - 08/27/07 07:22 PM Re: 4.0 jeep cherokee rough idle [Re: dwendt44]
rt_ponder Offline


Registered: 09/11/06
Posts: 64
Loc: over the edge....of the Sierra...
Got around to cleaning TPS. That helped alot! Checked for vacume leaks....none, checked ohms on everything around throttlebody......all ok! Wasn't really all that dirty, but dirty enough to cause the idle to sputter. Thanks all youz bitogers!!

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#965829 - 08/27/07 08:53 PM Re: 4.0 jeep cherokee rough idle [Re: rt_ponder]
mikeg5 Offline


Registered: 06/18/07
Posts: 1754
Loc: north carolina
good work Ponder

also take into account type of plugs and plug wires, distributor and cap..make sure they are champion plugs! all jeeps run on champions esp back then.. this is why i buy my stuff at a dealership bc its DEFF OEM speced. yeah you might pay an extra 10$ for all that but ---- come on! how often do you change that stuff?? so its worth it

also, check the idle control butterfly valve. make sure its clean around the edge of the butterfly and its surroundings. you will see a big black ring where stuff collects.. clean it good
_________________________
02 Toyota Tacoma 4 door 3.4 v6 4X4
150k miles. Amsoil in the diffies and tranny
05 Corrola LE 145k miles auto

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#965830 - 08/28/07 02:51 AM Re: 4.0 jeep cherokee rough idle [Re: mikeg5]
rt_ponder Offline


Registered: 09/11/06
Posts: 64
Loc: over the edge....of the Sierra...
Got that too.....it's as clean as a whistle!
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#965831 - 08/28/07 11:02 AM Re: 4.0 jeep cherokee rough idle [Re: rt_ponder]
novaracer69 Offline


Registered: 09/09/06
Posts: 100
Loc: ypsilanti michigan
seafoam it. thats what i do to my GC and it runs great for about a year then i do it again.

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#965832 - 09/21/07 03:13 AM Re: 4.0 jeep cherokee rough idle [Re: novaracer69]
rt_ponder Offline


Registered: 09/11/06
Posts: 64
Loc: over the edge....of the Sierra...
AAAArgh!! Still idles like ----. Now I'm having what feels like it's cutting out. Even on a light throttle, it feels like sputtering, only for a fraction of a second. Put new TPS,didn'nt change anything. Even mashing the throttle, there's a stumble...---- over???!!! Help.
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#965833 - 09/21/07 03:37 AM Re: 4.0 jeep cherokee rough idle [Re: rt_ponder]
Quest Offline


Registered: 12/19/04
Posts: 7357
Loc: beaver land EH?
check for vacuum leak. I know for a fact that mid~late 90s Jeep cherokee suffered from vacuum booster leak of some sort so you can try unplugging that vacuum line, plug it and see if that helps.
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#965834 - 09/21/07 10:04 AM Re: 4.0 jeep cherokee rough idle [Re: Quest]
novaracer69 Offline


Registered: 09/09/06
Posts: 100
Loc: ypsilanti michigan
what kind of plugs are you running?

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#965835 - 09/21/07 04:08 PM Re: 4.0 jeep cherokee rough idle [Re: novaracer69]
Greaser Offline


Registered: 02/13/03
Posts: 1992
Loc: Windsor,Ontario
Fuel pressure low?Fuel pump may-be on it's way out.Bad injector?Try a different brand of gas from a new gas station.Sometimes water in the fuel will give these symtoms.
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1999 Jeep Cherokee-
2001 Jeep Wrangler- both engines 4.0L & Rotella T5/T6 with Napa Gold Filters

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