I just had similar problems with my 05 f-250 recently, it turned out to be the ICP sensor, my truck didnt throw any codes, the way you can tell is if the ICP voltage is low, mine was at .82 volts, and for the ICP to be working properly it should be at 1.2 volts or very close to it, check the volts on the ICP if your scanner can read that, my guess is that it is your ICP.