Okay so after I start the engine on one of these cold Michigan mornings and she gets up to about a 90 degree ECT the 5.4 whistles. After she gets to temp and I start my daily drive it goes away but then if I park and leave her run, after a few minutes of a standing idle the whistle starts again.

My first guess in the game of troubleshooting is exhaust manifolds but just in case I'm wrong I wanted to jump in here for a bit to see if any of you seniors heard of this before. Happy Easter !

 

might be a manifold, but I would check all vacuum lines. They generally whistle and hiss

 

I have seen 2 different issues with engine compartment whistling.

My F150 was the IAC valve- replaced under warranty.

My brothers F150, it was the belt tensioner. Also replaced under warranty. Both are '03 5.4's.

Just some other things to look for other than your standad vacuum leaks.

Hope this helps.

 

thanks for the help guys I'll check it out.

And thanks for the support Ruger.