I have an '01 dodge ram 1500. When it starts in the morning, or when you run the A/C it makes a whistling sound from the IAC valve. Once the temp reaches 150 degrees or higher it goes away, but no matter what, when the A/C is on it makes the whistling sound. What causes this? What is the easiest fix? and what controls the IAC valve? If anyone can help I would greatly appreciate it.

 

How are you sure it coems from the IAC?

You could take it off and clean it with carb cleaner too

 

The best way I know of to find a vaccum leak and that is what it sounds like you have, is to take a can of carb cleaner and spray around your throttle body. If the idle changes when you spray a spot that means you found your leak. I don't know if that will help or not, just my $.02.