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Rough Idle, Red deposits on plugs?


Old 04-07-2003, 12:59 AM
Thread Starter
Join Date: Jun 2002
Location: Delavan, WI
Posts: 29
Rough Idle, Red deposits on plugs?

My 2002 FX4 (5.4L) has idled rough ever since it was new. Sometimes it's just a roughess/misfire that can be felt in the seat, and sometimes it's bad enough to make the tach jump.

There are no codes, and of course most trips to the dealer are answered with a "No Problem Found". However at the last visit, the mechanic showed me the spark plugs, which had a reddish deposit on the ceramic insulator. He was saying the only way I would see this is if I am putting something in my gas, which I am not. I buy my gas from the large Mobil station right next to the dealer, where they do all their fill ups, so if the gas was a problem, I think they would be on to it by now. By the way, a new set of plugs and boots was no help.

I've read many of the other rough idle posts, but I have some specific questions:

Has anyone ever seen these deposits?
Does anyone have a 2002 that idles rough like this?
Since mine is a 2002, it doesn't have the #4 coil issue..etc, so any ideas on what to look for?

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Old 04-12-2003, 04:23 PM
Thread Starter
Join Date: Jun 2002
Location: Delavan, WI
Posts: 29
Doesn't anyone have a newer 5.4 that idles rough?
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Old 04-12-2003, 05:56 PM
Senior Member
Join Date: Apr 2003
Posts: 260
Ash Deposits: light brown deposits encrusted on the side or center electrodes or both. Derived from oil and/or fuel additives. Excessive amounts may mask the spark, causing misfiring and hesitation during acceleration. Recommendation: If excessive deposits accumulate over a short time or low mileage, install new valve guide seals to prevent seepage of oil into the combustion chambers. Also try changing gasoline" so first order of the day is to try new gas stations. If that doesnt help, hit the dealer up about the valve guide possibility.
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