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Author Topic: xj 4.0l revs high and low.  (Read 2456 times)

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Offline 99xj

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xj 4.0l revs high and low.
« on: December 16, 2012, 12:28:53 PM »
Hello this is my first post in the forum. Yesterday noticed my jeep when idle for couple mins would try to stall then rev high. Also sometime while driving feel cutting out!!!

Since then today I have flushed fuel system and cleaned TB. Also replaced TPS sensor. But is still acting up.

Motor is stock besides gforce chip and throttle spacer. Please any ideas or help greatly appreciated
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99 xj 6.5 iron rock long arm 33's
02 tj 4' rough country 33's sold

Offline yellowjeep101

  • Budget Lift
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Re: xj 4.0l revs high and low.
« Reply #1 on: December 16, 2012, 01:04:46 PM »
Check engine light? If so, check the code. Check the code anyways, maybe your check engine light is burnt out. I'm thinking you have a o2 sensor that is done.
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Offline 99xj

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Re: xj 4.0l revs high and low.
« Reply #2 on: December 16, 2012, 01:20:25 PM »
the check egine is not on at this time and since started idle problem. But has came on and off over last couple of weeks
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99 xj 6.5 iron rock long arm 33's
02 tj 4' rough country 33's sold

Offline 99xj

  • Stocker
  • Posts: 14
Re: xj 4.0l revs high and low.
« Reply #3 on: December 16, 2012, 02:09:48 PM »
after reading some forum post i see could be IAC valve so just got one from napa I'll see if this is the fix
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99 xj 6.5 iron rock long arm 33's
02 tj 4' rough country 33's sold

Offline 99xj

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  • Posts: 14
Re: xj 4.0l revs high and low.
« Reply #4 on: December 16, 2012, 03:15:19 PM »
replace the Idle control valve. didnt fix it. now after jeep gets to running temp at idle it will act up rough idle. If I turn it off and back takes about 10 minutes of idling for it to do it again...
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99 xj 6.5 iron rock long arm 33's
02 tj 4' rough country 33's sold

Offline apeman

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Re: xj 4.0l revs high and low.
« Reply #5 on: December 16, 2012, 03:20:08 PM »
Most likely the upstream 02 sensor.
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Getting grumpier every day.
99 XJ - It's got sum stuff ,Noel free stuff..
98 ZJ - It's just ugly, but bigger than your Rubi

Offline 99xj

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  • Posts: 14
Re: xj 4.0l revs high and low.
« Reply #6 on: December 16, 2012, 03:35:09 PM »
Ok thanks I see yourself and yellow jeep think is the samething.  I am going to give that a try thanks to you both
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99 xj 6.5 iron rock long arm 33's
02 tj 4' rough country 33's sold

Offline 99xj

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  • Posts: 14
Re: xj 4.0l revs high and low.
« Reply #7 on: December 17, 2012, 03:26:55 PM »
Today I checked codes, Nothing, swapped o2 sensor main stream. But still when get to 100 temp will start to idle rough up and down. once turned off will run fine again for 10 mins or so.
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99 xj 6.5 iron rock long arm 33's
02 tj 4' rough country 33's sold

Offline WagoneerXJ

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Re: xj 4.0l revs high and low.
« Reply #8 on: December 17, 2012, 03:48:38 PM »
G force chip? That the resistor thing from ebay?
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98 XJ Sport 2 Dr, 3", 33's and Bushwacker Flat Flares
87 XJ Wagoneer 5", Dana 44, 34" Swamper TSL's
97 TJ 5.2 Magnum V8 swap, 4" and 33" MTZ's- GF's Jeep
84 Mustang GT-Built 351W 5spd
97 XJ - 3.5", 31" BFG. 370,000 KMS and counting!

Offline WhiteOut

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Re: xj 4.0l revs high and low.
« Reply #9 on: December 17, 2012, 03:49:50 PM »
Best place to start is to remove the chip.
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Offline 99xj

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Re: xj 4.0l revs high and low.
« Reply #10 on: December 17, 2012, 04:41:46 PM »
I removed it but  still does same either way. Totally stumped now.
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99 xj 6.5 iron rock long arm 33's
02 tj 4' rough country 33's sold

Offline 99xj

  • Stocker
  • Posts: 14
Re: xj 4.0l revs high and low.
« Reply #11 on: December 17, 2012, 04:43:00 PM »
the Gforce chip Im not too sure it was installed when I purchased jeep.
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99 xj 6.5 iron rock long arm 33's
02 tj 4' rough country 33's sold

Offline apeman

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  • Posts: 1012
  • not as grumpy
Re: xj 4.0l revs high and low.
« Reply #12 on: December 17, 2012, 04:58:15 PM »
Coolant temp sensor malfunction.
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Getting grumpier every day.
99 XJ - It's got sum stuff ,Noel free stuff..
98 ZJ - It's just ugly, but bigger than your Rubi

Offline 99xj

  • Stocker
  • Posts: 14
Re: xj 4.0l revs high and low.
« Reply #13 on: December 17, 2012, 05:05:45 PM »
where abouts could I located that under hood. I will give that a try thanks.
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99 xj 6.5 iron rock long arm 33's
02 tj 4' rough country 33's sold

Offline yellowjeep101

  • Budget Lift
  • Posts: 222
Re: xj 4.0l revs high and low.
« Reply #14 on: December 17, 2012, 08:33:24 PM »
I'm still thinking its your o2. I had similar issues and all it was was that sensor
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