Will crank and run but does not idle, there are no codes?

1989 CHEVROLET SILVERADO
270,000 MILES • 5.7L • V8 • 2WD • AUTOMATIC
Avatar
DSTHOE
  • MEMBER
  • 1 POST
Will crank and run but won't idle, there are no codes?
Dec 9, 2022 at 8:52 PM
Advertisement
Avatar
STRAILER
  • ✓Experienced Mechanic
  • 55,256 POSTS
This can happen when the engine has a vacuum leak or the idle air control motor stops working, here is a vacuum leak detection guide that should be used when the engine is cold only and the location of the IAC valve which you should replace if there are no vacuum leaks.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Check out the images (below). Let us know what happens and please upload pictures or videos of the problem.
Images (Click to enlarge)
Professional Diagram for 2CarPros Members
Click here to log in and view diagram.
Professional Diagram for 2CarPros Members
Click here to log in and view diagram.
Professional Diagram for 2CarPros Members
Click here to log in and view diagram.
Dec 10, 2022 at 4:25 AM
Avatar
DSTHOE
  • MEMBER
  • 1 POST
Replaced IAC still want idle, is there a way to check to see if IAC is communicating with computer? no vacuum leak.
Dec 12, 2022 at 4:41 AM
Avatar
STRAILER
  • ✓Experienced Mechanic
  • 55,256 POSTS
Yes, remove the IAC and then plug it in and turn the ignition on, the IAC should move outward or inward. Let me know.
Dec 12, 2022 at 4:42 AM
Join 2CarPros for free, one of the most advanced car repair communities on the internet. From first-time drivers to seasoned mechanics, everyone is welcome to reply, share details, and get better answers. You can add a temporary image or video first; uploads are limited to 20 MB.
Ask a Free Question
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.