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Discussion Starter #1
Hello men,

I have a 1999 XJ 4.0 4WD Auto. 170,000 miles. This is the problem...about a month ago I pulled into a parking lot and came to a stop and it just died. Started it back up, checked all gauges, everything looked fine, it purred like a kitten so i just assumed it was a hicup or bout of bad gas.
this evening the thing starts idling really high on me as I am trying to stop for a red light. The engine was actually working against me for a second. I came to a stop, threw it in neutral and the thing revs to about 1100-1200rpm. I tapped on the gas and it came back down to normal. After I put it back it gear it did fine as I accelerated. Then as I came to a stop it idled high again, became sort of erratic, I threw it in neustral and just watched the tach. It jumped around a little bit between ~800-~1100. This time I threw it in gear without tapping the gas and the sucker immediately died.
I have researched a few threads on here and I think I might start with the Idle control solenoid next to the TPS.

Is this my problem or do I need to consider anything else? Thanks!
 

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Discussion Starter #2
I forgot to mention one thing. The engine has been taking several more cranks to get it to start. It starts fine everytime, but it just takes it a little longer now. Any ideas guys? Thanks!!
 

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Discussion Starter #4
My guess would be the CPS (Crank Position Sensor)... when they start to go they cause those symptoms of which you speak.
Are they expensive? Should I get one through a dealer or will an autozone CPS do the trick? Im a little sceptical of those autozone Wells brand sensors and switches. I havent had the best of luck with their headlight switches.

Thanks for any further advice. I will go ahead and clean the IAC and replace the CPS and maybe check the TPS with the meter when I get the chance.

:cheers:
 

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I agree. CPS.

Mine has been doing that on and off for about a year.

Now would that cause a stutter on acceleration and the in-ability to get up to speed?
 

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Discussion Starter #8
hey guys, I pulled the whole throttle body off tonight. Took the IAC off and it was pretty caked with carbon. I cleaned it up along with the rest of the throttle body. Put it back together and it started right up! Idle was perfect. Drove it about ten miles and it idled perfect the whole time. Seems to me that this has solved the problem. I will keep you posted if anything changes or it starts acting up again. Thanks for all the help!!
 

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Discussion Starter #9
okay guys, here is an update. The Jeep runs great and idles great. The engine feels very powerful and normal. Now I am having some hard starting issues when the engine is cold. It takes a few more cranks than usual to start it up. Once it is running I have no issues, no stalling, no rough idle. I just got a bottle of Lucas fuel injector cleaner and have run through about half the tank of it. No improvement yet. I thought I might have some clogging fuel injectors. Is there anything else I might consider? Could it be a CPS or other sensor? Thanks for any help!!

Ray
 

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No other advice here.....

My problems came down to compression....

Low across the board, plus 50 PSI in cylinders #1 AND #5...

damn...:brickwall:
 

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Discussion Starter #13
Well crap, this morning my erratic idle started back up again. I think I will test the MAP sensor on the manifold. anyone know what the specs are on the ohmeter for that thing?
 

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Discussion Starter #14
Okay, I hate to revive this but I finally got a CEL last night. The jeep has been running great for me up until last night.

Here is what I have done so far. I cleaned the IAC and replaced the CPS. Everything seemed fine after that. Last night it throws a P0123 and P0122 code while driving about an hour away and begins to idle @ 1100rpm. Those codes tell me its the TPS. So I went to the parts store and bought one. I put it on the throttle body in the parking lot and started the jeep. The damn thing started idling erratically between 900 and 1100 rpm. WTF? I put the old one back in and everything ran and idled fine. So I returned the new TPS. I cleared the codes, engine light came right back on but I had no idling problems the rest of the night and all the way back home. THis morning the CEL is off, I ran the OBD II scanner again but the codes are still there. Does anyone have any clue as to what I can do with this now? Thanks again for any help.
 

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Pick up coil in the distributor. Finally fixed the same problem u have. It took 4 ever to finally throw a code on it because it was so erratic. My advice hit the boneyards grab all the common sensors for 20 bucks and trial by error. Easiest and cheapest way to do it. Discount part stores have cheap sensors, so go get OEM ones for pennies. Example...went through 4 autozone ignition coils and finally put one in from a boneyard for 5 bucks and problem one of the past.
 

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Discussion Starter #16
Guys, it was the butterfly in the throttle body!!!!! Over time the bearings have either gotten worn, or the shaft has been worn. The butterfly was being allowed during certain instances to be seated a little sideways while in the idle position. This allowed just enough air to creep through and cause a higher idle. I fiddled around with the idle set screw to get it to work with the new amount of play in the throttle butterfly, and now the Jeep runs fine. I have been driving now for several days with no issues.

So. A better fix is to either get new bearings or a new shaft, or to replace the throttle-body altogether.

I can't believe it was this simple.

THis is how I know:

I pulled into a parking spot. The engine was reving to 1200 rpm. I popped to hood and took notice that not any of the three cables leading to the throttle lever were tight. This leaves only a couple of things. IAC, or other bad sensor, right? WRONG!! I took the throttle leaver in my hand and forced it to close all the way. I felt the play in the bearing/shaft and once I closed it the engine instantly idle @ ~700-750 rpm.
 
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