• 1990 Vette - fast idle at start
  • 1990 Vette - fast idle at start
  • 1990 Vette - fast idle at start
  • 1990 Vette - fast idle at start

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  1. #1
    New Member
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    Default 1990 Vette - fast idle at start

    All,

    New here and experiencing the following with one of my cars:

    a. Upon cold start up, engine idles fast (upwards of 2,000 to 3,000 rpms) for about 10 or so seconds, then resumes normal rpms.

    What could cause this, a sensor?

    Any hints, assistance, or help is appreciated.

    Empty3

  2. #2
    1990 Vette - fast idle at start TedC's Avatar
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    Oct 2007
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    1989 Red Coupe
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    Empty3, Welcome to CAC. I would suggest getting a copy of the factory service manual. If you search this site for IAC, minimal air and idle hunting you will discover multiple possible causes like vacuum leaks, defective IAC, defective ECM, wrong PCV, lack of maintenance on the throttle body. There is no idle speed adjustment. The adjustment screw is for the minimal air setting (proper procedure to adjust available at this site). Hopefully it still has the tin cap, and no one adjusted it without knowing how it actually works. The ECM monitors and controls idle speed. On my 1989, 1100 rpm when cold, dropping to 600 rpm when the coolant reaches around 140 degrees.

  3. #3
    Member gmjunkie's Avatar
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    Quote Originally Posted by TedC View Post
    If you search this site for IAC, minimal air and idle hunting you will discover multiple possible causes like vacuum leaks, defective IAC, defective ECM, wrong PCV, lack of maintenance on the throttle body. There is no idle speed adjustment. The adjustment screw is for the minimal air setting (proper procedure to adjust available at this site). Hopefully it still has the tin cap, and no one adjusted it without knowing how it actually works. The ECM monitors and controls idle speed.
    Probly have a cracked vacuum hose somewhere or Faulty PCV,Leaking Throttle Body,Leaking EGR Valve, or Intake Gasket!!ECM and IAC can compensate for a slight leak somewhere,but can't do it at cold start till it runs for a bit! Check vacuum lines and for leaks around throttle body and intake manifold!!
    It's got so it seems to me that the Internet has created a lot more Horses A$$'s than we have Horses!
    junk!~!!
    Founding Member: 10 Corvettes Anonymous


  4. #4
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    Quote Originally Posted by gmjunkie View Post
    Probly have a cracked vacuum hose somewhere or Faulty PCV,Leaking Throttle Body,Leaking ECR Valve, or Intake Gasket!!ECM and IAC can compensate for a slight leak somewhere,but can't do it at cold start till it runs for a bit! Check vacuum lines and for leaks around throttle body and intake manifold!!
    Thanks TedC and gmjunkie, I was hoping for a quick 'it's this widget' type of answer : ) I'll start troubleshooting.

    Empty3

  5. #5
    Member gmjunkie's Avatar
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    Quote Originally Posted by Empty3 View Post
    Thanks TedC and gmjunkie, I was hoping for a quick 'it's this widget' type of answer : ) I'll start troubleshooting.

    Empty3
    May be nothing more than the intake or throttle body needing re-torqued!
    It's got so it seems to me that the Internet has created a lot more Horses A$$'s than we have Horses!
    junk!~!!
    Founding Member: 10 Corvettes Anonymous


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