Hello, I have a 2004 F150 w/ the 4.6. When I have the heater on defrost ( Turns the A/C on), The Truck's Idle will fall from about 800 Rpm to 500 Rpm then spike up to Almost 1000 Rpm and then it starts over again ( The whole Process takes about 30 seconds). As soon as I turn the Climate control to the Vent selection, the Floor selection or Off position the Idle Returns to Normal.

This only happens at Stop lights, Drive thru's, Ect.... Any Help or Idea's would be great.....


Thanks In advance..
Adam