Go for the wheels forget the ECU without something like headers or forced induction its a waste of your money.
It WILL be detected by the dealer as soon as the car is connected to the SDS the software is verified and if its been modified it is immediately flashed with stock software and your engine, transmission and if the dealer wanted even electrical system warranties are null and void. This is why people with cars that have been modded are open about it they take the warranty hit because most big name tuners offer warranties as good as OEM to them to replace whats lost from MB this also allows the owners to say keep away from XYZ control units they are not standard.
Never trust a salesman mate, wheels on the other hand great buy will give a noticeable difference in performance.
__________________ One thing you will learn with German cars - If it's simple it ain't happening. |