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  #1  
Old May 12th, 2004, 09:48
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Question Weird Idle

Over the past day my 89 xj 4.0 has been idling weird. When I left work yesterday and started it up it reved to like almost 3000rpm. I put it in gear and it stayed idled at around 1400 in gear. Normally in gear its around 700.
By the time I got to my house it was back to normal, but it kinda erratic, almost like a misfire. Today its doing the same thing but not quiet as bad, its still a lot higher than normal and not as smooth. Any ideas? Also, I have only owned this xj for a few months but every since I have had it the 2-3 shift has been very firm, almost neck snapping. But with the idle acting weird it not as bad, it feels almost normal.

Thanks for any ones input.
Scott
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Old May 12th, 2004, 10:09
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Re: Weird Idle

Two or three things can cause what you describe. An erratic vacuum leak, a bad throttle position sensor TPS, or a idle air controler IAC.
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  #3  
Old May 12th, 2004, 12:42
greenday9d1 greenday9d1 is offline
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Re: Weird Idle

My '92 XJ's idle was very strange when I first bought it and got it running again, it was a faulty TPS which was a very cheap fix at a mechanic.
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Old May 12th, 2004, 17:13
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Re: Weird Idle

Its usually a combination of the TPS and the IAC that causes the high idle-
there was a recall on the TPS`s of that year(I believe)- check with alldata, then your jeep dealer-.

If the TPS *ISNT* faulty- what happens is the IAC will stick just a hair open, the TPS wont kick back down...its usually just plain carbon poison. Every time I change the oil, I pull the IAC to clean the pintle, and check the TPS on my ohms meter for a clean sweep.
On my last 89XJ, I had two dead spots on my TPS- one was a hair under WOT, the other about 1/3 throttle-neither place I usually ran, so I left it.
My 89 MJ has one dead spot almost 3/4 through the sweep....If Im that deep into the throttle, I got problems.
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Old May 12th, 2004, 19:09
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Smile Re: Weird Idle

Thanks for all the info. I looked at the throttle body tonight, and it looked pretty gunked up. I imagine the iac is probably the same. Going give it all a thorough cleaning tomorrow after work and see what happens.
thanks again everyone.
Scott
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  #6  
Old May 12th, 2004, 20:11
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Re: Weird Idle

Pull the throttle body and clean it on a workbench. It will clean up much better than trying to clean it in place. Use a cleaner that is 'sensor and plastic safe' when cleaning the sensors. It might also be time to park at a parts store and start replacing vac lines one by one with all new hoses. We did that with our YJ and it solved a wealth of problems involving cracked and split hoses. I messed up and bought a bunch of hoses and then had to make repeated runs for the plastic L, T and Y connectors not to mention I had a bunch of hose sizes that I did not need left over.
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Old May 14th, 2004, 20:29
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Arrow Re: Weird Idle

I have the exact same problem. I changed the Idle Air Control Valve and the vaccum lines on top of the engine and still no luck.

So I guess my next question is - what is the TPS and where is it located and how do I test it?

XJ '89 In-Line 6 Automatic 4x4

Many thanks guys! Hope to fix this problem that's been haunting me for three years off and on.

John
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  #8  
Old May 15th, 2004, 04:23
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Re: Weird Idle

I solved this problem on mine; the manifold bolts around #6 were just a tad loose, enough to cause a vacuum leak. It idles like it should now.
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Old May 15th, 2004, 18:26
Trail-XJ Trail-XJ is offline
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Re: Weird Idle

i just checked my intake bolts and my #6 was way loose, tightened all the bolts and i'm finally good to go!
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  #10  
Old May 19th, 2004, 14:15
gz32 gz32 is offline
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Re: Weird Idle

how tight shoud the intake bolts be?

thanks
curtiss
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  #11  
Old May 19th, 2004, 15:28
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Re: Weird Idle

This can also be the warning signs of a failing cps... Mine did that in the early stages of failure. Is it ever hard to start? If so CPS might be going...
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Old May 19th, 2004, 18:45
gz32 gz32 is offline
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Re: Weird Idle

I replaced my cps, and tps about 4 months ago
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  #13  
Old May 20th, 2004, 06:06
Trail-XJ Trail-XJ is offline
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Re: Weird Idle

i dont' know the tightning spec for the intake bolts but i got them pretty tight, mine were so lose i am surprisec they didn't fall out!
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  #14  
Old May 20th, 2004, 06:54
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Re: Weird Idle

I suggest you find an FSM.
Intake 20-25 ft. lbs
Exhaust: middle nuts 30 ft lbs. outside nuts 23 ft. lbs.
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