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frostbiker

2000 Grand Cherokee Rough Idle Issues

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I'm hoping the brain trust of this fine forum can help nail down a problem for me.

 

My 2000 Grand Cherokee V8 ran fine friday morning, but, 10 hours later, had difficulty starting. Idle was very rough and RPMs were below 1000. Got it towed home and thought maybe the fuel pump/filter may have an issue. Changed the filter this morning. Pump and filter are fine. Oil doesn't show signs of water. Coolant is not leaking and still full. Haven't checked the gas for water, but that is high on the list. Same with plugs.

 

I'm pretty sure that is the order of things to eliminate before sending to the mechanic. Am I missing anything?

 

Your help is greatly appreciated.

 

And, yes, I've been researching online and through the various forums.

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First thing I would do is check it for hard codes, most of the chain parts stores can loan you a reader. Most common culprits I can think of would be TPS and CPS. Also check for obvious things like vacuum leaks and dirty or poor grounds.

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You might also want to pull the battery cables off and clean the connections. About a month ago mine had dirty connectors and didn't want to start or idle. Towed it home and after a cleaning everything is fine. They are fussy about their battery connections.

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yes clean TPS and battery connections before sending it away - also clean the IAC.

 

and even if you don't have a check-engine light on, do the key trick to get any stored codes and let us know if you have any.

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Ran the codes this morning and didn't have any. Check engine light was on for the fuel evap sensor. Cleared it out and hasn't returned.

 

Instead of having to replace all the individual sensors, would it be best to start by replacing/refurbing the PCM?

 

Battery connections are clean. No sign of corrosion on them.

 

My punch list includes:

Check fuel for water

Oil change (make sure no water)

Check spark plugs

 

I should add, the rough idle sounds more like a miss than anything else.

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Oh, and please remind me of the "key trick" to get the stored codes.

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Oh, and please remind me of the "key trick" to get the stored codes.

 

i have seen once where my code reader didn't return anything but the key trick did, so might as well check...

 

you just turn the key from OFF to RUN (not START) 3 times and leave it on the third time in the RUN position, then watch the odometer. it should read out any codes one at a time then say DONE. if it just goes right to DONE then no codes are present. if you don't see codes or DONE then you didn't do it right ;)

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Thanks. I wasn't too sure if I used the OBD right today. Had to input make/model/year for it to read codes. I'll do the key trick after work tomorrow and see if something pops up.

 

I'll keep ya'll posted.

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checked codes with the key trick this AM. None. Drained all oil and pulled the filter last night. Started the truck to make sure all the oil was out. The idle was rough, but much better than what it was when the Jeep went Tango Uniform last week. Dropped in 4.5qts of Royal Purple and let it sit for 10 minutes while I pulled the contacts on the PCM (clean, no visible problems). Turned the engine over and the idle was gawdawful. Worse than without the oil. Going to test the fuel right now and then check the spark plugs.

 

Any thoughts on the oil/idle symptoms?

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