I have a 2005 F150 with a 4.6L engine with 117,000 miles and recently the idle will alternate between 500 rpm to 1000 rpm. I changed the sparl plugs and fuel filter at 90,000. I have been reading about the IAC Valve but I dicovered that it only time the idle is affected is when the compressor is engaged. Does anybody have any sugestions. Is it the IAC or a Vacume Hose?

 

I don't believe you have an IAC valve - 05's have an electronic throttle.

 

I discovered that today so do I just need to clean the tps?