4.2 runs rough

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Aug 13, 2009 | 08:56 PM

Harry Thompson

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4.2 runs rough

I have a 1998 F150 with the 4.2 V6. I just replaced all four O2 sensors and several others that were showing codes on the diag-computer. The check engine light was on before the replaced parts and is still on? For a couple of weeks after the sensor replacement it idled fine. But now it idles rough and this rough idle is intermittent from rough to almost stall. It is a bother but has not stalled yet. Seems to be worse when the engine is hot. Generally I take good care and the engine is in good condition. Also no codes show on the computer? I suspect the idle control or MAS, but this is a guess? Please help.

Aug 13, 2009 | 09:03 PM

Ultramagdan

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From: Kansas

Sounds like your IAC is acting up.

Aug 28, 2009 | 04:14 AM

oneeyedmac

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Please forgive my ignorance, but what is an IAC?

Aug 28, 2009 | 06:16 AM

torkum

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From: Mount Juliet, TN

Idle Air Controller= maintains air coming in to the engine when the throttlebody is closed.

Aug 28, 2009 | 07:01 AM

oneeyedmac

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thanks, much appreciated.

Aug 28, 2009 | 07:48 AM

bokker

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From: uk

hi, check the rubber boot under the manifold in the middle. it perishes coursing a vacuum leak and many of the problems you describe. good luck bokker.