IAC....maybe

[ghost111]

This is a 1999 3.0.
When starting the car cold, the idle goes to about 1650 and slowly works it's way down to 700 as the car warms up [1650 seems too high] and sometimes when starting the car warm the idle sits at 300 and will stay that way unless I drive away and nail the gas once. Then it returns to normal idle.
Does this sound like the IAC needs a good cleaning? Thanks.

[Mister_Perkins]

Your car will typically always idle high at first. If your IAC were stuck, you would experience the throttle being very low the entire warm up (Around 300-500 RPM typically).

Sounds more like your having a heat-soak issue to me.. Cleaning the Intake is always a good idear though

heres an example of a bad IAC. Notice how at the beginning of the video the car is vibrating so badly the door panel is shaking

You Tube

You Tube

[ghost111]

Originally Posted by Mister_Perkins

Your car will typically always idle high at first. If your IAC were stuck, you would experience the throttle being very low the entire warm up (Around 300-500 RPM typically).

Sounds more like your having a heat-soak issue to me.. Cleaning the Intake is always a good idear though

heres an example of a bad IAC. Notice how at the beginning of the video the car is vibrating so badly the door panel is shaking
http://www.youtube.com/watch?v=iUsSH8JUrGw

OK I can live with high RPM on cold start. But the intermitent 300 RPM warm starts is making me suspect that the IAC is sticking. What is heat soak? Thankyou

[Mister_Perkins]

Heat soak is when you turn your car off while hot, and the motor continues to maintain a hot temperature .. The biggest factor here is the ambient heat from the motor staying hot allows other things to raise in temperature higher than they typically would while driving, or when the fans are running.

This is just a theory, but what may be happening is your motor is continuing to stay hot and causing a temporary Vacuum leak when you turn the car off. (whether it be an Injector or a Vacuum line).

You can try to Seafoam the intake manifold and see if it helps though

[ghost111]

Heat soak is interesting in theory. However , sometimes when I cold start on a warm day it just idles at 300 until I drive it and nail the throttle hard, once. Then everything is OK. [strange?]

[Mister_Perkins]

Could be the IAC, like I said Seafoam it and see if it changes. Carbon deposits are always building up in the motor so its always a good idea to clean it out.