Genuine OEM Audi Engine Valve Spring, part number 03F109623. This critical engine component is responsible for closing the engine valves after they have been opened by the camshaft, ensuring precise valve timing and proper combustion chamber sealing. It is located within the cylinder head, around the valve stem. Using a genuine OEM valve spring guarantees the correct spring rate, material fatigue resistance, and durability, which are vital for maintaining engine performance and preventing catastrophic valve train failure.