I have an 01 f-150 with the 4.6 liter triton. When standing still with the truck in drive, foot on the brake (lol). The idle drops and then goes back to normal over and over. It does this with the a/c on or off, but does not do it in park or neutral. Any ideas?

 

Try cleaning the IAC (idle air control) valve.

 

Thanks man! A project I'll soon be undertaking, I'll let you know how it goes.

 

That link shows how to pull off the whole Throttle Body and clean it too. Although not a bad idea, just cleaning the IAC is MUCH easier.

You don't need to pull the TB, just undo the three 10mm bolts holding the plastic cover, and two 8mm bolts holding the IAC. It comes off easy, and you just need to undo the wire going to it.

Total job is 10 minutes or so (1 beer).

Good Luck