Popping in exhaust
I've done the water trick also, it works. Like MVR said, operating temp- 2,500rpm. just trickle the water in slowly so it vaporizes. The hydrogen molecules stick to any carbon deposits in the combustion chamber while carrying the oxygen molecules with. The extra oxygen heats the carbon deposits causing pre-detonation(before the plug fires) in the chamber. This is why the motor needs to be revved. The pre-detonation loosens the deposits and they blow out the exhaust.
BEFORE you try this, it is HIGHLY recommended that you back your car up to a WHITE chebbie! hehe