I had this same problem with a Steeda CAI. After going to the dealer, getting the bama tune adjusted, getting rid of the bama tune and getting a Steeda tune. My 2010 GT did the same thing. Finally got rid of the intake, and rocked a Steeda tune for the stock airbox for awhile. I finally bought the airraid cai about two months ago from American Muscle, and no decel and RPM surging. I think that my 2010 GT and yours may just not like the particular CAI that is installed.

 

The weird thing with mine is these problems just started randomly a few weeks ago. Would the car necessarily throw codes if something was wrong with the MAF or TPS? I'm wondering if maybe it's a sensor issue. Since Ford hasn't been very helpful, I guess I need to continue taking this into my own (and this forums) hands. Thanks.

 

I testing the MAF, TPS sensors with an ohm meter, everything checked out in spec. Cleaned MAF sensor, throttle body, changed fuel filter, spark plugs, tested alternator. When I put the stock air box back on the decel issues went away. I even tested the car with the stock tune and the STeeda CAI (which you aren't supposed to do) and it would have the decel issues. The only thing that caused the decel problems was the CAI. My car literay did not like that particular CAI. Maybe you are having the same issue with yours.

 

I'd recheck the connections/fittings for the CAI-to-intake tube and intake tube-to-TB. Any air in-leakage will throw the PCM for a loop. There have been issues with CAI connections before and not just Steeda.