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Old 12-18-2009, 05:28 PM   #1
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jeeps cold= ruff idle until warm, what gives

I have been trying to trace this bug for awhile now, tried some sea foam in the gas, new spark plugs, etc..
When the jeep is cold like first thing in the morning, i start it up and the idle goes high( say around 1K), but then a few secs later it will drop off likes its going to die/rpms get real low, and then it will catch itself, idle goes back to around 1K but sounds/appears ruff, and it may frop down again, just depends on what kind of mood its in, Knock on wood it has never just died, idle goes up and down and is ruff..

Now the kicker, if the jeep is warm, or i just drove it to the store and then started it back up it runs fine, Very slight ruff idle but nothing like when its cold??? what else should i be looking for, or looking at?

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Old 12-18-2009, 09:37 PM   #2
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i have the same problem.. at first a few guys i worked with and i (one was a retired mechanic) thought it was either a tps sensor or a o2 sensor but the more i read about em the more my mind changes.. and also it hasnt thrown a code yet

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Old 12-18-2009, 10:26 PM   #3
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I'd start by looking for a vacuum leak. Use a BURNABLE carb cleaner or better yet propane.

When it's cold extra air is getting in that the computer didn't plan on, it's not adding enough fuel, end up too lean.

Once it's warmer, the O2 sensor "sees" it's too lean, so the computer compensated for it.

Check vacuum lines, the gasket below the throttle body, and the hard one - the manifold gaskets where it attaches to the head. It's difficult to get the carb spray down onto the leak - you might try shooting it from the bottom. Or, propane will get down there.

You MUST do it while its running rough cold, else you'll be chasing your tail (when you hit the leak it'll change RPM and run better for a moment.) It may take several tries.

Let us know what you find.
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Old 12-19-2009, 07:03 AM   #4
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thanks

Just so everyone knows this is a 2003, its somewhat fuel injected, has a throttle body setup, however that might be something to look at is vacuum lines, the weird thing is the problem doesnt stick, it doesnt do it if the motor is warm, and the ruff idle, loss of rpms only happens for a few seconds, 1 or 2 times then the idle will go back up, almost like the computer is compensating for the cold air and advances the throttle. but i will look into vacuum lines.
It also did not do it when i ran seafoam in my last fuel fill up??
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4.56 gears are finally in
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Old 12-19-2009, 02:54 PM   #5
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That's the nature of the beast. The computer does what it can to compensate for it.
There's a time during the transition from cold to warm when the computer isn't quite on-line yet.
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