Rough idle at start question....opinion before I start spending money. - JeepForum.com

 
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post #1 of 2 Old 08-23-2010, 09:48 AM Thread Starter
Cali04LJ
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2004 LJ Wrangler 
 
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Rough idle at start question....opinion before I start spending money.

I live in the central valley of CA where it gets pretty hot. This last week I went wheeling up in the Sierra National Forest. I was headed up into the foothills right before a long steep climb up the grade into the mountains. I stopped to top off my gas tank when I had the problem. After getting gas, I started my Jeep (04 LJ w/ auto trans) and it was idling really rough. Felt like it was only firing on 2 or 4 cylinders. I gave it a little gas and after about 10 seconds it smoothed out. I got a little nervous so I let it sit for about 10 minutes then started it again and it did the same thing. I sat for a few minutes and everything was ok. I headed up the hill with the o/d off like I usually do and the rest of my trip was smooth sailing. My thinking is that it was a cooling issue. On this particular day it was 105 degrees. I had the a/c on until I started up the grade. I turned it off when the issue happened. The foothills are a slight change in elevation but not much (1500 to 3000). The grade goes to 7000 pretty quickly. Once I left the gas station and starting climbing everything was fine. The temperature does change drastically once you start climbing up the hill(105 to 80). Where I ended up was at 9000ft and was 70ish. My LJ has a 3.5 RE lift on 33's so I know the trans is under a load compared to stock.

I have been thinking about adding a transmission cooler for awhile and wanted some opinions. Do you think it could have been part of my issue? I could feel how hot the floorboard was thru my tennis shoes. I also thought maybe the thermostat stuck for a second then opened up which caused the rough idle.

The jeep has 44k miles. I bought the jeep with 40k miles. It was bone stock when I bought it and had never even seen a mud puddle. So the lift and tires are recent. I have been wheeling it regularly with no issues however this was the hottest day when I was climbing uphill.

So before I go and replace the thermostat and add a trans cooler, I thought I would hear what everyone has to say.

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post #2 of 2 Old 08-23-2010, 10:07 AM
alilredjeep
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Quote:
Originally Posted by Cali04LJ View Post
I stopped to top off my gas tank when I had the problem. After getting gas, I started my Jeep (04 LJ w/ auto trans) and it was idling really rough. Felt like it was only firing on 2 or 4 cylinders. I gave it a little gas and after about 10 seconds it smoothed out. I got a little nervous so I let it sit for about 10 minutes then started it again and it did the same thing. I sat for a few minutes and everything was ok.

My LJ has a 3.5 RE lift on 33's so I know the trans is I also thought maybe the thermostat stuck for a second then opened up which caused the rough idle.
I'm not real up to date on the newer Jeeps but I do know that the thermostat would have already been opened up from engine heat soak while you were stopped for gas, so its not likely to be a 'stat.
I'm thinking maybe an oxygen sensor since you were at an elevated height and the computer may have had to readjust the computer settings to compensate.
I'm just guessing though.
Thats just my

It also helps others if you would please fill out your profile.

Eddie
RED JEEP CLUB MEMBER #92

'92 WRANGLER, 2.5 Litre, 5 Speed, Rag Top, Superwinch LP8500, Cepek 130W Driving Lights, 31x10.50/AT with no lift, Of course! It rubs!
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