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Unread 08-28-2014, 10:09 AM   #1
MattFerguson14
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2002 KJ Liberty 
 
Join Date: Aug 2014
Location: Mesa, AZ
Posts: 22
rough idle

Hello again. I recently bought a 2002 liberty limited edition with the 3.7 V6. When sitting at a red light, the truck seems to idle a little rough. Nothing major, but i can feel a little rumble throughout the vehicle. I just got the truck with 140k on it and it's been like this since i got it, so I have nothing to compare it to. Are these jeeps known to have a bit of a rough idle, or could it be a misfire?

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Unread 08-28-2014, 08:12 PM   #2
Leeann_KJ
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Have you ever replaced the plugs? NGK copper is the OEM plug (and coppers are all you should put in it) and they last about 30k.

Also, you could have bad motor mounts. The rubber dry rots and cracks due to heat, UV and vibration.
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Unread 08-29-2014, 07:53 AM   #3
remmons
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I'm curious to see what his plugs look like, especially since his Jeep as 140k miles and who knows when the plugs were last changed.
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Unread 08-29-2014, 08:44 AM   #4
MattFerguson14
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I'm going to do a tune up on her this weekend. I'll post a pic of the old plugs. I haven't pulled them yet but I'm curious to see what they look like also. Can I pick up NGK coppers at autozone?
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Unread 08-29-2014, 08:56 AM   #5
MattFerguson14
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Also, remmons, i checked the rear upper control arm and couldn't find a problem. I think I may have a worn motor mount as well. The truck definitely has a slight misfire, i can hear a light ticking in the exhaust. I'm hoping this tune up will fix it.
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Unread 08-29-2014, 08:59 AM   #6
MattFerguson14
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Leann, do those Yokos perform well off road?
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Unread 08-29-2014, 12:12 PM   #7
remmons
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Quote:
Originally Posted by MattFerguson14 View Post
I'm going to do a tune up on her this weekend. I'll post a pic of the old plugs. I haven't pulled them yet but I'm curious to see what they look like also. Can I pick up NGK coppers at autozone?
Yes, you should be able to pick them up from any auto parts store.
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2002 Liberty Sport 3.7. 2.5" lift.

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http://www.jeepforum.com/forum/f12/i...t-case-989208/
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Unread 08-29-2014, 12:17 PM   #8
remmons
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Quote:
Originally Posted by MattFerguson14 View Post
Also, remmons, i checked the rear upper control arm and couldn't find a problem. I think I may have a worn motor mount as well. The truck definitely has a slight misfire, i can hear a light ticking in the exhaust. I'm hoping this tune up will fix it.
I'm sure that there are others who will check for a worn motor mount differently than I do, but this is what I do.

I put wheel chocks on the rear wheels, apply the parking brake, hold the brakes, place the shifter into drive, then reverse while an assistant watches the engine for movement. Or I have the assistant perform the motions while I observe the engine movement. Using jacks and pry bars work, but for me this is real-world engine movement mimicking driving conditions with the engine under load.
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2002 Liberty Sport 3.7. 2.5" lift.

I am by no means a professional. I know just enough to get myself into trouble.

http://www.jeepforum.com/forum/f12/i...t-case-989208/
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Unread 08-29-2014, 12:49 PM   #9
Leeann_KJ
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Quote:
Originally Posted by MattFerguson14 View Post
Leann, do those Yokos perform well off road?
Haven't driven it rock climbing or anything, but on loose dirt, mud and gravel they're awesome.
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Unread 08-29-2014, 03:43 PM   #10
MattFerguson14
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Thanks remmons, I'll perform the test after work. And thanks for the info Leann. I need a new set of tires and am strongly leaning toward the Yokos. I'm not looking to climb any rocks either. Mostly just deep loose dirt and loose gravely hills where i'm at in AZ. Wish there was more mud!
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Unread 08-29-2014, 08:55 PM   #11
The_Dealer
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Quote:
Originally Posted by remmons View Post

I'm sure that there are others who will check for a worn motor mount differently than I do, but this is what I do.

I put wheel chocks on the rear wheels, apply the parking brake, hold the brakes, place the shifter into drive, then reverse while an assistant watches the engine for movement. Or I have the assistant perform the motions while I observe the engine movement. Using jacks and pry bars work, but for me this is real-world engine movement mimicking driving conditions with the engine under load.
I do it pretty much the same way, with a few differences. I chock the front tires very good, and have an assistant put the jeep in 1st/low. I get them to hold the brake, then stab the gas quickly and let off quickly. Think power-braking, but quick revs under load. I watch the mounts to see if the engine is moving abnormal amounts. Usually it's the drivers side that goes bad from torque-twist. Then do the same in reverse. Reverse will amplify passenger side mount movement. Also, get in there to see the condition of the rubber. I've found that in tight spots where I can't get a good look I stick my cell phone down there and take some pics. You'd be surprised at how well that works. Pry bar method is also works pretty good.

OP, I have a feeling it's your rear upper, even though u said there wasn't any play. It would be worth removing it to check the bushings. The sleeve tends to separate from the rubber, and there's usually separation of the voids. The bushing isbeing put into a bind whenever the arm is anywhere other than level. Even at stock ride height (which has no doubt sagged a good bit), the upper arm isn't level and more than likely pointing upwards. The sleeve could be halfway ripped from the rubber, but due to binding it's possible not to see any play when prying on it.

Edit:
Drive your Jeep a few miles (far enough to reach operating temp), and feel the ujoint caps and see if they are hot. Could be a ujoint drying out causing your rumble as well. What speed does it start? Does it start to do it from a stop, or does it begin at a certain speed? Is it rpm specific? When you start to feel it, does it go away when u put it in neutral? Does it get worse when u put It in neutral and Rev to 3k rpm?

As far as your misfire, I'd do like others have stated and change the plugs to NGK copper (V-Power). Make sure u check the gap, as ive had some not gapped correctly. It would be a good time to pull your tb off and give it a good cleaning. Remove the tps and iac, and clean the iac tunnel very good. A small toothbrush will come in handy. BTW, if my tb was considered "normal amount of dirty" for a KJ, u will need about 3 cans of tb cleaner. A new pcv valve wouldn't be a bad idea either. Inspect all the vacuum hoses for cracks or broken t's/nipples.
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Unread 08-29-2014, 08:59 PM   #12
Leeann_KJ
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Pic of the Yokos when I got them


And mounted
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Unread 08-29-2014, 09:47 PM   #13
The_Dealer
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I forgot to mention, with the mileage on your rig I recommend picking up some Redline SI-1 fuel system cleaner. O'Reilly's, Pep Boys, and Advance keeps it in stock, but you can order online and get it fairly quick. It has one of the highest PEA contents available, and is one of the best fuel system cleaners out there. I've had great results using it, and since using on my 98 cobra I now swear by the stuff. It's not a misfire cure in a bottle, but definitely a good maintainance habit.
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