Intake whistle

[dirt,rust&tears]

At 232,000, my '91 ex blew the head gasket this week. I need something a little more reliable now. I test drove a 2000 F150 this morning. I noticed a high pitch whistle, sounding like an intake thing at certain rpms. I couldn't hear the sound if I put it in park and revved the engine, just in a certain range while driving. It's the 5.4 engine. It has a K&N intake, and I was wondering if the sound could be from that, or if it could be the IAC and how big of a deal that would be. Any help would be greatly appreciated.
-matt

 

[DB_1]

Sounds like a classic dirty IAC valve, some people have had luck cleaning the IAC with contact cleaner or elec parts cleaner (same thing i think). If that doesn't work then a replacement is necessary. You can find them for around $50-$100 depending on which brand you go with...Motorcraft will obviously be the most expensive.