Rough idle after spark plug change...
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This is a discussion on Rough idle after spark plug change... within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; So i went to change my spark plugs the other day and after everything was installed back together i had ...

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    Rough idle after spark plug change...

    So i went to change my spark plugs the other day and after everything was installed back together i had a rough idle?? So i took the new plugs out to make sure it wasn't those and re-installed the original plugs, still rough idle. I'm POSITIVE everything is installed correctly and all plugs/coil packs are on tight. I've heard some people say this could be a vacuum leak?

    I mostly feel the idle down in the pedals. but i can also hear it slightly. anybody have any ideas on what this could be?

    Another note. the idle gets worse when i use my power windows. as if the extra strain on the alternator is bringing it down, however it's much worse than it ever used to be.

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  3. #2
    Registered User teflon_jones's Avatar
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    How are you positive everything is installed correctly.

    What did you remove / reinstall other than the plugs, the coil packs, and wiring?

    Year/model/mileage/maint history?
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    UnBanned Sinister's Avatar
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    Did you use dielectric grease?

    Did you make sure that the battery leads are connected tightly/securely?

    Have you checked that you plugged your MAF back in?

    Did you make sure to put that grounding plate back on cylinder 4?
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    sorry i guess i didn't provide much info,

    2004 wrx, 97,000 miles on it. Maintenance is all up to date and done on time if not a bit early for safety.

    Back to the issue. I did plug my MAF back in, i even cleaned it with MAF cleaner. All battery leads are secured tightly. I didn't use Di-electric grease, and i don't know what your talking about with the grounding plate on cylinder 4? i didn't see anything come off with my coil pack?

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    Moderator Donkey's Avatar
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    Obviously you did something to cause a change. Go back and check over everything you removed and around it. No CEL?
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  7. #6
    UnBanned Sinister's Avatar
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    absolutely need to use dielectric grease. That can cause not enough electricity to pass through the coil into the plug, and possibly cause hesitation. There is a plate that comes off of the 02 sensor on my car that grounds into the number 4 plug. Don't know if this is only on the 06+ or not.
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    Sinister, dielectric grease is non-conductive. It will NOT pass electricity from coil to spark plug. It will keep oxidation from happeneing and moisture from interfereing between connections and I used it on my plug connections for this reason.

  9. #8
    FMS
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    Did you check the spark plug gaps sir? even though the gap is usually correct from the manufacturer, its always good to check.
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    Quote Originally Posted by FMS View Post
    Did you check the spark plug gaps sir? even though the gap is usually correct from the manufacturer, its always good to check.
    ^ What he said. I bought some NGK GP Platinum plugs at autozone and were .044 in the box... Glad I checked and corrected them down to .031

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    I would check your spark plug happing aswell as the vacuum lines goinh to the pcv. They co.e loose sometimes

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