MAD BMW Exhaust Valve Controller EssentialMAD Valve Controller Essentials Everything You Need. Total Control. No Guesswork. Take full control of your exhaust sound with the MAD Valve Controller Essentials a simplified, plug and play solution designed around the valve positions enthusiasts use most every day. Unlike the factory system, which constantly opens and closes the exhaust valves based on drive mode, throttle input, and emissions requirements, the MAD Valve Controller lets you lock the