Hello out there. I've got a problem. I have a 08 f150. When my truck is at idle with the a/c on, the rpms fluctuate from 500-800 and sometimes higher. This happens when it's in PARK or in DRIVE with a foot on the brake. When in DRIVE, it will sometimes fluctuate so forcefully that it will make the truck lurch forward. The truck only has 34,000 miles so its still under warranty. My local Ford dealership has the truck right now and has had it for the past 4 days. They have no clue. Please help! Thanks

 

Anytime the AC Compressor cycles on it will raise the RPM..just how much depends on the vehicle. It does this so that the engine won't stall under the load of the compressor. If your dealer has no clue..it's time to take it somewhere else

 

Check for leaks in the intake hoses or connections between the mass air flow sensor and the intake. Sometimes this can affect the idle.

 

I bet Ford already checked this.

 

Vac leak, could be bad intake gaskets. Ive seen a few go bad and cause a surge.