Whistle under hood?

[TheCraic]

Hi guys/gals,

Very informative site. I've been using for about a year and having a lot of luck with the problems I have had so far just by using the search function. This time though I do not seem to be able to get to the root of my problem which is:

A high pitched whistle from under the hood which does not change in pitch with engine speed. I thought it might be the IAC, but when I switch on the lights the whistle disappears. Does this sound consistent with a dirty/malfunctioning IAC? If not, any other ideas.

Many thanks.

1999- 5.0 V8 Limited

 

[dreamr]

I am betting it is either the IAC or a vacuum leak.

 

[ExplorerDMB]

Vaccum leak is your most possibly of the whistle

-Drew

 

[gijoecam]

The IAC makes the most sense to me. In essence, it IS a vacuum leak. It's just the vacuum leak that allows the engine to continue running, that's all. If it is the IAC, when you switch on the lights, there is more load placed on the alternator. The IAC then needs to open the orfice slightly to allow more air in to compensate for the extra load and maintain the engine idle. Turn the lights off and the whistle comes back, right?

Now, you mentioned that it doesn't vary with engine speed.... that's a little weird as when you crack the throttle, it doesn't draw anywhere near as much air through the IAC and it should stop.

Here's another thought: Have you recently installed a new belt? Is it by any chance a Goodyear Gatorback? If so, I'd put my money there.

-Joe