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Unread 12-25-2013, 05:02 PM   #1
chrisshreves
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XJ Rough Idle

My girlfriend's Cherokee has been giving her idle problems for awhile now. Most recently, she complained that while driving, it started acting strange and hesitating. She pulled it over, shut it off, and started it back up. She explained that when in park or neutral, the idle was very high (around 2k-2.5k). When she would put it in gear, the idle dropped dramatically. She said it idled very low, which I would guess would cause the "rough idle". This problem has been occuring more frequently, and even once while traveling about 6 states away from home.

Recently, I replaced the spark plugs with Autolite APP986 Double Platinum (recommended on JF). I also cleaned the IAC, cleaned throttle body, replaced crankshaft position sensor, and replaced the throttle position sensor.

I am wondering if these problems are related to the coil pack assembly? I have been debating replacing it, but it is pricey. Also someone on JF said that aftermarket sensors are garbage, which I have a hard time beleiving because many people don't buy Mopar sensors. Is it really nessisary to buy a Mopar sensor?

I would really like to get this resolved, because if not, then the Jeep will likely be junked for a chevrolet by her father, which neither her or myself are in favor of. She likes the Jeep, but doesn't like the reliablility because of how the Jeep reacts to this issue. Any help would be appreciated!

A few end notes:

Jeep: '00 XJ 4.0L AW4 NP231
Injector cleaner used every 1,500 miles.
Oil changed 50 miles ago, 5w-30 Penz.

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Unread 12-25-2013, 05:31 PM   #2
uberxj92
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Hi and welcome.
Is the check engine light on?
You need to pull the codes. Go to big name parts stores. They usually do it free.
You may want to contact a jeep service center and make sure that the higher end plugs are right. To the best of my knowledge regular champion plugs are the best for a 4.0.
10w30 oil for our jeeps.
It may be those plugs.
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Unread 12-25-2013, 05:53 PM   #3
pismo61
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The plugs are right.As far as sensors go Mopar are the ones to get and I did buy a new NAPA coil pack that was just as bad as the bad origonal Mopar that was in my 2000 cherokee.I returned it and got a new Mopar coil pack(rail) and it ran like new again.Just my experience with some of this stuff.
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Unread 12-25-2013, 05:56 PM   #4
chrisshreves
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The check engine light came on when it happened, but I have not had a chance to see if it is still on at this current time. I'm pretty sure the plugs are fine, They are practically brand new, gapped at .035, and are correct for the distributorless ignition systems found in 1999.5+ 4.0L engines. And the owner's manual calls for 5w-30 oil for the current temperatures where the Jeep is operated so I doubt that is the issue. I'm just wondering if it could be maybe a MAP sensor, or a TPS or more likely the coil pack assembly itself.
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Unread 12-25-2013, 06:09 PM   #5
chrisshreves
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This is exactly what I was looking for. Were your symptoms similar before you changed the coil pack?
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Unread 12-25-2013, 06:18 PM   #6
RisingJeeper
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Sounds like I am having very similar issues. Did the problem progressively get worse? My engine reliability gradually decreased over about 6 months then we did a tune up and replaced corroded spark plugs and wires, distributor cap and rotor. It ran great for about a week and then began getting worse again, this time it seemed to deteriorate more quickly. Did you have this sort of result with your attempts to fix?
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Unread 12-25-2013, 06:20 PM   #7
RisingJeeper
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And what's the coil pack? Is that only for distributorless jeeps?
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Unread 12-25-2013, 06:48 PM   #8
chrisshreves
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If your tuneup included a cap and rotor, then your jeep does not have a coil pack. Coil pack assembly engines do not have a distributor with a cap and rotor. The coil pack assembly is actually not as good as a distributor.
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Unread 12-25-2013, 07:04 PM   #9
RisingJeeper
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Alright that's what I thought. So I'm most likely looking to fix something other than what you already have replaced and cleaned. I've been thinking maybe fuel pump, have you had any issues with yours?
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Unread 12-25-2013, 07:51 PM   #10
webbs54
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Did you ever think you maybe got a faulty TPS?? My jeep was doing the same thing until i replaced the tps. i have read that you are taking a shot in the dark if you dont buy oem sensors?
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Unread 12-25-2013, 10:11 PM   #11
chrisshreves
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Faulty TPS could be it. And I have also read that aftermarket sensors are garbage. Might just go down to the stealership and order the coil pack and map and tps and iac, replace them all, and see what happens. Tired of messing around with this thing. Plus my other cherokee is going to take on a 1,500 mile trip here soon so I really need to turn wrenches on it before I take it on vacation.
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Unread 12-26-2013, 11:45 AM   #12
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Quote:
Originally Posted by RisingJeeper View Post
And what's the coil pack? Is that only for distributorless jeeps?
Yes. 99.5-01 xj
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Unread 12-26-2013, 11:48 AM   #13
uberxj92
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Pull the codes. Even if the cel is off. They will be stored. CJtim has the best philosophy on here pull codes and then spend money. It nay be just one simple thing.
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Unread 12-26-2013, 12:05 PM   #14
chrisshreves
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Thats a good idea. I will take it to Avanced as soon as I get a chance. Hopefully it will have codes stored! I wonder if there is a code for the coil pack assembly?
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Unread 01-15-2014, 08:20 PM   #15
chrisshreves
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Just for a follow up, I did get a code off the Jeep. Ended up being a bad TPS from AAP. It lasted a whopping 3 months. I swapped it out and went to the stealership and order the $230 coil pack assembly in hopes of clearing up a very faintly rough idle.
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idle issue , rough idle , throttle position sensor

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