High idle
Thread Starter
Junior Member
Joined: Aug 2024
Posts: 7
Likes: 1
High idle
Hi I have 1989 f150 xlt lariat it has the 4.9l inline 6, I currently have the iac unplugged due to high startup idle. However my main concern is when I start the truck it idles at 1000 and then as I drive it it go a little higher to about 1300 - 1500 and then never goes back down.
Senior Member
Joined: Jul 2007
Posts: 3,805
Likes: 480
From: Cape Girardeau MO
Welcome to the site!
First pass, suggest looking for vacuum leaks in the various hoses or gaskets on the intake past the butterfly. Ensure the main throttle butterfly is able to close completely and repeatedly, looking for crud obstructions with the cable or the spring or within the butterfly area - DO NOT FOOL with the throttle stop screw.
That era had challenges with the idle air control (IAC) solenoid crudding up, generally leading to a surging idle though - ensure the innerds are clean enough so that the piston travels smoothly from end-to-end without any hitches. Carb cleaner works well to clean things up.
First pass, suggest looking for vacuum leaks in the various hoses or gaskets on the intake past the butterfly. Ensure the main throttle butterfly is able to close completely and repeatedly, looking for crud obstructions with the cable or the spring or within the butterfly area - DO NOT FOOL with the throttle stop screw.
That era had challenges with the idle air control (IAC) solenoid crudding up, generally leading to a surging idle though - ensure the innerds are clean enough so that the piston travels smoothly from end-to-end without any hitches. Carb cleaner works well to clean things up.
