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This is a strange one

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Old 04-11-2012, 10:19 AM   #1
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2001 Jeep Cherokee 4.0. Intermittent problem with rough idle and backfiring on start up then normal idle and running. Problem occurs on start up cold and hot just not all the time. Replaced battery and checked connections. Charge rate is nearly 14 volts. Replaced idle control valve. Any suggestions are appreciated.
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Old 04-11-2012, 10:24 AM   #2
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Ya, if you look around the site this has come up a couple times. I have the same issue, some say if your plugs aren't gapped properly that could have something to do with it. Is your check engine light on? Mine keeps throwing a misfire code. Still trying to figure out what the issue is.
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Old 04-11-2012, 08:56 PM   #3
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Checking for codes is always a good start, since it will give you an idea.
The rough idle can be caused by several things. May need some more info, including:
- Does it run fine, so no backfiring/stalling whilst driving?
- how long does it take for the rough idle to settle?
- when was last tune up done?

Rough idle on startup is not related to your battery. A possible cause could be fuel 'leaking' from the injectors. With this , the rough idle is caused by the engine getting rid of the extra fuel and should usually settle when thats done, 1-2 minutes.
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Old 04-11-2012, 09:56 PM   #4
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i get the same exact thing man, what usually helps it is running a bottle a lucas oil fuel stabilizer through the system.
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Old 04-11-2012, 10:04 PM   #5
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From what I've gathered from searches it might have something to do with the injectors. My symptoms usually occur only after the truck has been driven shut off and then restarted after a half hour or more. On a cold start this usually never occurs unless i dont allow the engine to warm up a bit which once it does the hessitation/misfire goes away, as far as the first scenario i find that it'll usually clear after 1 of two things 1-riding it out for about 10-15 minutes 2-flooring it for a few seconds works wonders and clears the problem up, not too sure if this is bad for the engine though. I cant remember exactly but i believe it has something to do with vapor accumilation in the cylinders after the truck is driven, shut off for a short period of time then restarted. Again this is one main cause i found but its worth looking into. Ill see if I can find the thread with this info and post a link
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Old 04-11-2012, 10:20 PM   #6
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this thread has some of what im talking about http://www.cherokeeforum.com/f2/99-x...r-loss-119514/
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Old 04-12-2012, 06:34 PM   #7
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Could be your CPS going bad.. They can cause intermittant issues like you describe. (Crankshaft Position Sensor)
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Old 04-15-2012, 10:00 AM   #8
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Thank you for all the responses. Glad I'm not the only one experiencing the problem. The engine smooths out in 10-15 seconds after start when warm. The odd thing is it doesn't happen all the time and about the same When starting cold.
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Old 04-15-2012, 11:31 AM   #9
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search heat soak...post 5

Last edited by freegdr; 04-15-2012 at 03:28 PM.
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Old 04-15-2012, 12:35 PM   #10
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*If it happens with BOTH a hot engine and a cold engine, I'd suspect a leaky fuel injector

*If it only happens with a HOT engine, then "heat soak" is a possibility; not uncommon especially on the 00-01 XJ.
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