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Thread: 89 SC idling around 4K?!?!

  1. #1
    Join Date
    Sep 2011
    Location
    Brandon, MS
    Posts
    19

    89 SC idling around 4K?!?!

    I was driving down the road and out of nowhere my car just revved up to about 4K rpm. I drove it home like that and when I start it now, it immediately jumps to about 3.5k-4.5k rpm and does not idle down. Any ideas on where to start looking for the problem? Could this be an easy fix... or should I just take it to a shop? Any insight would be appreciated!

  2. #2
    Join Date
    Dec 2007
    Location
    Salem, OR
    Posts
    6,295
    Floormat hanging up?

    Checked the linkage at the throttle body? Is the cable still connected?

  3. #3
    Join Date
    Sep 2011
    Location
    Brandon, MS
    Posts
    19
    No floor-mats, and all the cables and the linkage look fine...

  4. #4
    Join Date
    Dec 2007
    Location
    Salem, OR
    Posts
    6,295
    Pull the air intake and confirm the throttle plate is closed with engine off - note the position of the lever on the outside - is it at rest, against the stop? ...then fire it up and see if that changes.

    Still no joy, pull the connector off the IAC, then fire it up...it should struggle to idle.

  5. #5
    Join Date
    Sep 2011
    Location
    Brandon, MS
    Posts
    19
    Ok, I haven't looked at that, yet... I'll check it out tomorrow when I have more light! Thanks for the info KMT! I'll post an update once I know more. I really appreciate the help.

  6. #6
    Join Date
    Sep 2011
    Location
    Brandon, MS
    Posts
    19
    Started car, No change in throttle position, no change when IAC removed

  7. #7
    Join Date
    Dec 2007
    Location
    Salem, OR
    Posts
    6,295
    wow...4k rpm with the throttle plate closed - ouch. IAC doesn't sound like it's doing it's job - might be a severe vacuum leak there.

    Do you know where the supercharger bypass valve assembly is? Up on the intake, generally behind the supercharger hat/outlet?

    Note the lever's position with engine off, then start it up and see if it moves/closes.
    Last edited by KMT; 09-29-2017 at 12:08 AM.

  8. #8
    Join Date
    May 2002
    Location
    Dallas, TX
    Posts
    5,641
    If the IAC is good, then when you unplug it, the car will struggle to idle.. If it is bad, then unplugging it would result in no difference.

    Remove it.. look inside.. I'd be certain that the bellows is cracked..
    Last edited by TbirdSCFan; 09-28-2017 at 11:40 PM.

  9. #9
    Join Date
    Aug 2004
    Location
    Panama city
    Posts
    443

    change iac

    change out iac anyway i went through this years back on a 90 new iac from az was junk so i never considered that as an option finally switched out with a junkyard IAC AND ALL WAS WELL. hope it helps. leaned lesson oNly oem IACS FROM NOW ON

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