Okay, I have an issue on which I would like some input from the forum. Now that cold weather has come to my area, I am getting an intermittent whistling noise from my engine bay. It only shows up when the engine is cold and only under SLIGHT load at 1800 to 1900 RPM and around 44 MPH. It has vacuum leak written all over it, although the engine runs smooth during this time. What has me concerned is that when the engine warms up, I can't replicate the problem... which makes me think that when cold (contracted) the noise will occur and when warmed up (expanded) the noise does not happen. So I am asking for input on possible causes of this behavior. I am thinking maybe the plastic intake manifold , rather than simply a hose. Anyone ever experience this? Suggestions, possible causes or things to check are appreciated!

2003 Edge 3.0L Flex 4X2 Auto Trans

 

Usually vacuum leaks can't be heard like that, a whistling sound that is.
I would look for a leak in the throttle body tube and/or where it seals on the throttle body itself.
After it warms up, it stops because the leak seals itself off due to the rubber getting soft.
Just a thought.

 

IAC(idle air control) Valve has a Vent on the side with a cap

Picture of IAC Valve here: IAC Idle Air Control Motor Valve for Ford Taurus Truck Lincoln LS Mercury V6 V8 | eBay

Round cap in the center, it covers a vent that allows air behind the valve to get out or go in as valve moves.
It can make a whistling noise if IAC valve seal leaks, it is not technically a vacuum leak because the whole IAC Valve is a "controlled" vacuum leak in that respect.


Also the 3.0l Cam synchronizer bushings wear out, this will make a higher pitch sound, could be confused with whistling and would occur at certain RPMs and times, cold hot ect.....

 

Interesting. I assumed vacuum leak because it doesn't sound like a squealing belt or bearing noise. Weekend coming up, so I will investigate your suggestions. Thanks guys! :)