i have a 2000 f150 lariat with a 5.4 litre V8
there is a noise coming from near the fire wall on the passenger side, like a low pitched wine that changes with the rpm, its only noticeable from idle to about 1100 rpm's. what is it?

 

could be a vacuum leak. spray some carb cleaner around the vacuum hose connections in that area, if the engine speeds up you have found it.

 

Check your IAC valve.

 

i think it is the IAC valve because the sound is only generated when my foot is off the gas and it goes away when i even touch the pedal, so do i need a new IAC valve?