Well putcmondamnit said:Resetting the ecu doesn't actually make your car faster by itself, the learning program built in the ecu will attempt to learn your driving habits for the next 500 or so miles (maybe less, maybe more) and recalibrate tuning details ( I say tuning details because the specific actions it takes, be it adjustments to fuel, air etc. specifically is beyond the scope of my knowledge.) to suit your driving style.
So if you reset the ECU and drive with a top speed of 55mph, and never rev the engine over 3k rpm chances are the ecu will not make your car faster because it will "tune" itself to your "conservative" driving style.
But if you are the heavy footed, speed freak like a few of us are, and you reset the ecu and drive your car hard for 500 or so miles, your ecu will tune itself to your full throttle, balls to the walls style and end up being faster than the "conservative" one.
Resetting the ECU, at least been helpful in getting your IS to understand when you add bolt on type mods to your car. For example resetting your ecu after installing intakes and exhausts and even headers may help your car learn to recalibrate itself to these mods.
Hope it helps, if I'm wrong...sue me, i'm no mechanic ...just an enthusiast trying to help out.