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  #1  
Old 01-17-2002, 08:36 AM
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Default XJ Revving Problem???

Hello All,

Got this intermittent problem w/ the wife's Cherokee.
Every now & then when you start it, the engine rev's straight to 3000rpm. I've fiddled with the accel. pedal when it does this, but it won't idle down. You can go ahead & take off in 1st and the rpm will go to normal, but when you press the clutch pedal it goes back to 3 grand. Then with no apparent reason everything goes back to normal.
Also, if you turn the engine off right when it first rev's up, "sometimes" it will not do it on the 2nd start, but sometimes it will. I suspect it is some idle-up solenoid sticking or something but thought I'd ask.

Anybody experienced this & what did you do to correct it?

Thanks in advance--

OILBURNER tim.justice@ipaper.com
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Old 01-17-2002, 08:41 AM
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Default Re: XJ Revving Problem???

Think a few of us have and you are right on the idle stepper motor which is located on the throttle body is sticking. Mine does the exact same thing but not very often-I should get on that.

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Old 01-17-2002, 08:55 AM
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Default Re: XJ Revving Problem???

So a thorough T.B. cleaning ought to help!

OILBURNER tim.justice@ipaper.com
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Old 01-17-2002, 08:58 AM
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Default Re: XJ Revving Problem???

My '87 does it about once every four or five weeks. As it is reving I get out and un plug the stepper motor at the carb. It goes to normal idle and dosn't do it again for several weeks. I've sprayed it with carb cleaner but it dosn't seam to have helped. The day I bought it, it stuck right in the middle of the emission inspection and they wanted to fail it because of that but I talked them out of it.

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Old 01-17-2002, 04:25 PM
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Default Re: XJ Revving Problem???

You may want to try cleaning the TB and the TPS as well. If that dosen't do it you may need to replace the TPS. Seems to be a very common occurance.

89 Chreokee Laredo 4.0L
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Old 01-17-2002, 05:29 PM
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Default Re: XJ Revving Problem???

I have had this exact same problem as you explained it.
It seems the problem lies in the throttle body.
Take the air intake hose off the throttle body, get some carb cleaner, start the motor, and clean the TB real well.
This fixed my problem.
I cleaned my TB in March and have not had that problem since.
Hope this helps.

TX 4X4 club DFW Chapter
'96 XJ / '46 CJ-2A
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  #7  
Old 01-18-2002, 02:02 PM
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Default Re: XJ Revving Problem???

There are two potential problems. The first and most likely is the idle stepper motor on the TB. On shut down, the ECU moves this stepper motor into a postion to assist on startup. When the engine starts, the ECU uses this stepper motor to control idle speed. It operates the same as the idle adjustment on a Carb. In some cases it can get sticky which is why cleaning it helps.

The other posiblity (unlikly) is the TPS (Throttle Pos Sensor). It could be reporting a bad pos. Usually, this will also cause drivability problems.

John...southern CA
84CJ7, 3"lift, 32"BFG, 4.10's, ARB Rear, Detroit Front, Solid Axle's, Durabak, York Air

They say we learn by our mistakes......I guess thats why we are all so smart.
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Old 01-18-2002, 02:09 PM
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Default Re: XJ Revving Problem???

Its all about the TB... its a pretty common problem. i had it happen on Both of my 4.0's... a good cleaning should take care of it... if not, clean again. goodluck

Hall

i like jeeps... i've had my share of them
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  #9  
Old 01-19-2002, 02:21 AM
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Default Re: XJ Revving Problem???

When the hose to the TB from the MAP sensor comes loose on my 87 it does that. Check your vacuum hose.


[b]IF IT'S NOT DIRTY YOU'RE DOIN' IT WRONG
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