yeah, it could vary well be the FPR. its vary possible that your current regulator is not responding well when it sees no vacume and you car could actually be leaning out. or it could be the other way around and its dumping to much fuel in to soon and bogging it. you should have a friend follow behind you and see if a bunch of black smoke come out while its doin not responding durring exceleration. if so, that means your running way to rich. Also, you might want to make sure that everything is still calibrated correctly on your SAFC