Engine Management is the way to go, ecu or stand alone, the exhaust is letting it breath better so now you are hitting fuel cut, you running fmic an what you running .8,.9?? I ran .9 on standard ecu and exhaust, ran fine when i fitted the blitz ecu but started creeping once i fitted the free flowing system So ended up porting then putting the tongs on and hold 1 bar all day long John