LOST JEEPS :: View topic - Rough idle on '98 Wrangler

I have an odd situation that I'm trying to track down on my TJ and I need some assistance or advice. The TJ I have is a '98 manual with a 4 cylinder engine. When I am coming to a stop with the engine out of gear the RPMs drop very low and the engine will chug but as soon as the Jeep actually stops the idle returns to normal. I have no problem while in gear driving down the road. I've replaced the fuel pump, idle air control valve, spark plugs, wires, rotor cap, and rotor button but the issue still exists. I also get a check engine light occasionally which is apparently a misfire on cylinder 2 (according to diagnostics, slightly more voltage is required to fire that cylinder on occasion).

My current thought is that I may need to replace the coil pack as it's not been replaced in a very long time. This seems like a perfect job to perform during this long weekend but I can't find any instructions on where the coil pack is or how to replace it. I've read that it's easy but I can't find directons on where the pack is on a '98 TJ. Any assistance in locating the coil pack would be appreciated and any other advice on where to look to track down this idle issue is also welcome.

Author:	meduncan [ Wed Dec 31, 2008 4:35 pm ]
Post subject:	Rough idle on '98 Wrangler
I have an odd situation that I'm trying to track down on my TJ and I need some assistance or advice. The TJ I have is a '98 manual with a 4 cylinder engine. When I am coming to a stop with the engine out of gear the RPMs drop very low and the engine will chug but as soon as the Jeep actually stops the idle returns to normal. I have no problem while in gear driving down the road. I've replaced the fuel pump, idle air control valve, spark plugs, wires, rotor cap, and rotor button but the issue still exists. I also get a check engine light occasionally which is apparently a misfire on cylinder 2 (according to diagnostics, slightly more voltage is required to fire that cylinder on occasion). My current thought is that I may need to replace the coil pack as it's not been replaced in a very long time. This seems like a perfect job to perform during this long weekend but I can't find any instructions on where the coil pack is or how to replace it. I've read that it's easy but I can't find directons on where the pack is on a '98 TJ. Any assistance in locating the coil pack would be appreciated and any other advice on where to look to track down this idle issue is also welcome.

Author:	JJsTJ [ Wed Dec 31, 2008 4:42 pm ]
Post subject:
Lucky day! http://colorado4wheel.com/allmanuals/Jeep/TJ/ Hope that helps.

Author:	Ms5490renegade [ Wed Dec 31, 2008 9:14 pm ]
Post subject:	Re: Rough idle on '98 Wrangler
meduncan wrote: I have an odd situation that I'm trying to track down on my TJ and I need some assistance or advice. The TJ I have is a '98 manual with a 4 cylinder engine. When I am coming to a stop with the engine out of gear the RPMs drop very low and the engine will chug but as soon as the Jeep actually stops the idle returns to normal. I have no problem while in gear driving down the road. I've replaced the fuel pump, idle air control valve, spark plugs, wires, rotor cap, and rotor button but the issue still exists. I also get a check engine light occasionally which is apparently a misfire on cylinder 2 (according to diagnostics, slightly more voltage is required to fire that cylinder on occasion). My current thought is that I may need to replace the coil pack as it's not been replaced in a very long time. This seems like a perfect job to perform during this long weekend but I can't find any instructions on where the coil pack is or how to replace it. I've read that it's easy but I can't find directons on where the pack is on a '98 TJ. Any assistance in locating the coil pack would be appreciated and any other advice on where to look to track down this idle issue is also welcome. i have the same problem with my renegade. every now and then when i slow down, the car darn near shuts off. when i stop the rev's go to about 1000 then it goes to normal. and my check engine light keeps going on and off. i have never changed my spark plugs though. let me know ig you figure out the cause

Author:	meduncan [ Sat Jan 03, 2009 11:38 am ]
Post subject:
Thanks for the link. That information is extremely helpful. I've changed out my coil pack and while the idle is better it's still not perfect. I'm going to remove the Platinum +2 spark plugs that I had put in and put some standard plugs back in to see if that addresses the rest of the idle issue. Here's some back story and my own reasoning on the issue, I had swapped standard plugs out for Platinum +2 plugs and when I did so I noticed that the idle issue became noticeably worse. After changing the coil pack the idle issue with the Platinum +2's became less pronounced but it's still there. So my thought now is that there just isn't enough of a spark in my TJ ignition system to jump the gap on those Plats. Since I noticed an improvement by changing the coil pack and retaining the Plats I believe that swapping back to properly gapped standard plugs will completely eliminate the idle issue. I'll try swapping plugs today and post up the results.

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