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Thread: New Spark Plugs -- Weird Idle

  1. #1
    E500E Guru emerydc8's Avatar
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    New Spark Plugs -- Weird Idle

    As preventative maintenance, I just replaced my three-year-old factory plugs with same. The old plugs actually looked very good. After the new plugs were installed, when I started the car it started hunting all over for an idle. Restarted it and it seems to have gone away.

    Are these computers sophisticated enough to know the difference between new and old plugs and re-adapt to a better or different spark? Either that or maybe I disturbed a vacuum line as I was replacing the plugs.
    Last edited by emerydc8; 4 Weeks Ago at 09:03 PM.
    Jon D.
    1994 E420
    1995 E420

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  3. #2
    .036 Hoonigan™
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    Re: New Spark Plugs -- Weird Idle

    Jon, no... these computers are not sophisticated enough to know the difference between new and old plugs. It may have been a fluke, but it wouldn't hurt to double-check the vacuum and PCV hoses / tubes.

    Dave M.
    1997 E420 (Bugeyes)
    1994 E420 (Blondie)
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    1992 500E (Mach 5)
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  5. #3

    Re: New Spark Plugs -- Weird Idle

    For safe measure, make sure you are getting spark at every cylinder.
    Its rare, but sometimes a spark plug wire gets damaged when pulling them off.
    Last edited by Stevester 500E; 4 Weeks Ago at 09:37 AM.

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  7. #4
    E500E Guru emerydc8's Avatar
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    Re: New Spark Plugs -- Weird Idle

    Thanks, guys. I'll check it out. That was a new one for me. It's running smooth as silk now, so I don't think it's misfiring.
    Jon D.
    1994 E420
    1995 E420

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