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Thread: 93 SC dies during KOER test

  1. #1
    Join Date
    Dec 2002
    Omaha Nebraska

    93 SC dies during KOER test

    Hello all,
    Working on my sons 93 SC auto, we have a strange issue while trying to pull codes KOER. Checking codes due to an intermittent/temporary rough idle/misfire after a warm start. Iíve searched a few times with no concrete findings so far.

    KOEO tests come back clean, 111,111.
    During the KOER test, the engine revs to about 2000 RPM (I believe part of the balance test) as it normally would. Actually seems to hang there for a while and seems much higher than my 90, but Iím not aware of a time limit for that test or exactly what the high RPM should be. Eventually the idle reduces slightly above normal idle, then it suddenly dies. Doesnít sputter, shuts off like we turned the key off. Donít get any CEL sweeps during the KOER test until after the engine dies, then we see:
    412 unable to control high rpm test.
    538 insufficient change in RPM. Suspect because we donít get the sweep to goose the throttle.

    Ran the test several times and does the same thing every time- engine just shuts off shortly after returning to idle.

    Ive run the KOER test many times on my 90 AOD, am I doing something wrong with the 93? Haynes manual process doesnít differentiate between years.

    Thanks for your help,

  2. #2
    Join Date
    Apr 2002
    Madison, Ohio
    Sounds like a vacuum leak. If you aren't getting any CEL, then most likely you aren't going to learn anything from the code check anyway, but overall the symptoms point to a vacuum leak.
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

  3. #3
    Join Date
    Dec 2007
    Salem OR
    I agree, sounds like a vacuum leak.

    What happens if you pull the connector at the IAC, engine warm, and then attempt to start?

    Done any work to it lately? Any mods, like a chip?

    Not sure I'd worry about the code reading question at this point, just take the 11s for what they're worth, make a note, and move on.

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