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Old 04-03-2014, 03:54 AM   #1
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air box

Hello all!
I'm new here and have a problem with my engine. I own a 2004 ford focus ztw station wagon. I pulled out the air box thinking I could replace the filter... Ooops. Put it back on and now my car idles really high. So much that when I apply the brakes it revs before I come to a stop and keeps me moving forward. I noticed that there is a hose connector at the bottom of the box, but don't see that a hose goes to it. Is the problem that I missed connecting a hose there? Or did I undo something else. It ran fine until I removed and replaced the box. Any help would be greatly appreciated. Thanks

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Old 04-03-2014, 06:58 AM   #2
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1. There should be a hose from right side of the valve cover (just above the spark plug wires) that runs into the bottom of the airbox.

-this is not causing your idle problem.

2. Double check you plugged the MAF back in if you unplugged it to remove the filter.
3. Disconnect your negative battery terminal for 5-10 minutes this should reset your ECU and let it re-learn the idle settings.

-That should fix your problems
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Old 04-03-2014, 10:06 AM   #3
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Moved to General Tech. Chat, best place for mechanical problem answers.

Welcome to FF!

I'll add to double check everything is connected correctly. You may have pulled another tube loose that's connected to the resonator box you removed.
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Old 04-03-2014, 12:06 PM   #4
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Originally Posted by pmitchell View Post

... I noticed that there is a hose connector at the bottom of the box, but don't see that a hose goes to it...
You are not the first person to be fooled by that hose nipple sticking out from the resonator. Ford did that to remind us that they too have a sense of humor. That nipple does not have a hole inside it, so there is no air escaping.

You need to remove the resonator again, here is why... The resonator sits on top of the MAF tube. In-between the resonator and the MAF tube is a large rubber seal. When the resonator is re-installed, it is awkward, and the rubber seal can get pinched & damaged and create an air gap.

When I first got my Focus, I found a tiny-tiny piece of rubber stuck inside my IAC valve. This debris was causing idle problems like you have reported (and a few other symptoms too). Soon after, I found the resonator rubber seal was mutilated. Bought a new rubber seal at Ford.

You've got to ask yourself one question: Do you feel lucky? -and could you really drive a Focus ATX Wagon?

Last edited by Marde; 04-03-2014 at 12:10 PM. Reason: added pic
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Old 04-04-2014, 07:54 PM   #5
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How high it revs? I'd go with SlowestST suggestion. Check MAF. If it does not help, then check map sensor, temperature sensor, iscv valve... if the issue is not related, then it might be throttle position sensor, even lambda can do that. Resonator alone is not causing this, I have removed the resonator and there is only a hole now. There is absolutely no difference what so ever except the sound is slightly different.
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