Hello all. I have an 03 Screw 4X4 with a 5.4. I traded a buddy of mine for a MAC cold air kit and corresponding 75mmTB. After putting it on my truck, I have a very pronounced high pitched whistle just off idle. I may go back to my stock TB to see if it goes away, but it didnt whistle on his truck. I have no leaks in the system and there is no gasket hanging over in the air path. I even took it off and filed the throttle blade to try and eliminate the sharp edges. I do not think it is the CAI as my dad has the same one minus the TB on his 03 F150. For what it is worth, these parts along with my Magnaflow made a dramatic improvement in power. Considering I have 305's, i really felt it. Any ideas??

 

The only time I get a whistle/howl is when it is really cold out, and I thought it had something to do with the IAC. Are you sure all vacuum lines are correctly routed and connected?

 

Yeah, there are only the two lines (large ones) that run over to the intake tube. I even hose clamped them to be sure. The idle is perfectly smooth and low where it should be. The whistle comes through the filter.