Having read several comments on resetting the ECU, I remain unclear about the function of the ECU and why resetting it is significant. I am not even clear what it is, but suspect it is an Emissions Control Unit. How does it work? Does it continually retune the engine based on driving habits? Will it retune the engine of an air filter is replaced, as with a K&N? What exactly does resetting it do? Is it something other than the computer chip? Are there, or will there be aftermarket performance chips available for the G35?