1990 Vette - fast idle at start

[Empty3]

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

 

[TedC]

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.

 

[gmjunkie]

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!!

 

[Empty3]

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

 

[gmjunkie]

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!