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post #1 of 2 (permalink) Old 07-22-09, 06:50 AM Thread Starter
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04 Expedition Idle problem

I just bought a 04 expedition xlt and last night it started and issue that when I have it in P (Park) or when stopped at a light, the rpm idles from .5 to 1000 by itself back and forth also as it was going back and forth you would see the lights inside dim and come back in conjuction with the idle rev, also service engine light came on, also this morning while at the light and with the rocking back and forth of the rpms the battery light started blinking and the car turned off. after pushing it to the side and trying for a couple of minutes it started backup and I was able to at least get to work.

I also noticed that when I don't have my foot on the brake there is an air like noise comming from the pedal arm and if I press the brake the noise goes away. It sounds like if a big air leak is comming from the brake pedal when its not pressed.

I've cleaned the MAF and IAC and still the same issue, the Autozone Computer says its the 2 front 02 sensors, they also told me it could be the throtle sensor.

Any suggestions please help.
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post #2 of 2 (permalink) Old 07-23-09, 03:56 PM
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Re: 04 Expedition Idle problem

The O2 sensors can cause a rolling idle. However a vacuum leak can as well. Just behind and below the IAC valve (depending on the type of motor you have) there is a vacuum line that plugs on to the manifold. I have seen this line collapse and cause idle issues. I have included a simple drawing of the vacuum line. Caveat- It may or may not be on your motor. I can't remember if this was on the 4.6 or 5.4. Maybe someone else will.

FYI- You may have more than one problem. Fix what you can see is bad first. The O2 codes may be set because of the vacuum leak but it is normal for them to go bad as well.
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