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Discussion Starter · #1 ·
I have a 2004 Wrangler Rubicon. 4.0, 5 spd, 147000 miles. The Jeep runs and drives great, except at idle. The idle is rough. Just slight pressure on the throttle smooths it out.

Anyone?
 

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2004 is a long time ago. Lots of miles of vacuum lines that can and do dry rot and leak. A vacuum leak will affect the idling of the vehicle more than other times. I would first visually inspect all rubber hoses from front bumper to rear. If none are dry rotted and cracked, lose, fallen off, missing, etc., TO INCLUDE ALL THE ONE'S INVOLVED WITH THE FUEL TANK and it's smog control systems. Something to remember, a dry, crusty, hard and non-flexible hose will leak even though it's completely on its port. I would replace any of those you find.

If you didn't find any obvious culprits, then I would take off the large hose going to the vacuum booster of the master cylinder. Plug it off completely and see if that doesn't smooth out the idle after a second. A pin hole in the brake booster diaphragm will be very hard to notice unless eliminating it completely. If it still doesn't smooth out the idle, start unplugging each and every vacuum hose, close off the leak with rubber port plugs and eliminate each and every vacuum hose individually.

It's a lot to do, but I'll bet you'll find the culprit sooner or later. Luck!!
 

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I have a 2004 Wrangler Rubicon. 4.0, 5 spd, 147000 miles. The Jeep runs and drives great, except at idle. The idle is rough. Just slight pressure on the throttle smooths it out.

Anyone?
That particular problem is typically caused by a dirty/sticking IAC (idle air controller). Try this... with the engine running at IDLE rpms spray an aerosol throttle body cleaner into the throttle body. Only at idle rpms will the cleaner be pulled through the IAC to clean it. The engine will die, just keep restarting it and spraying more cleaner into the throttle body. Raising the rpms to stop the engine from stalling while spraying the cleaner will cause the cleaner to bypass the IAC and not clean it. The IAC is the engine's sole source of air at idle rpms so when it gets dirty, and they do, it will either make the idle rougher or it won't be able to run at all without giving the engine more gas which opens the throttle body valve plate to give it more air.

A vacuum leak raises the rpms, it won't reduce them.
 

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Discussion Starter · #5 ·
Thank you for the information. I will try that. So you disagree with the previous post, that it may be a vacuum leak?
 

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I have the same issue on my 06 Rubi, but it only happens a few times a month if that. Not sure what the issue is. It goes away after a few revs.
 

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I have the same issue on my 06 Rubi, but it only happens a few times a month if that. Not sure what the issue is. It goes away after a few revs.
Possible intake manifold gasket or other vacuum leak that seals once the engine heats a little?

Ideally you'd use a smoke generator when the engine is cold to check for air leaks.
 

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You definitely need to clean the IAC. I would clean the throttle body good, and the sensor in the intake hose close to the throttle body. Just did mine the other day and found the sensor in the intake hose was covered with black gunk. After everything was cleaned, my engine is running much smoother.
 

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Along with all the other advise, check the engine and Transmission mounts.
 
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