Genuine OEM Audi Accessory Drive Belt Idler Pulley, part number 07L903389B. This component is crucial for the engine's accessory drive system, guiding and maintaining the correct tension on the serpentine belt. It ensures smooth and efficient power transfer to accessories like the alternator, power steering pump, and air conditioning compressor. The pulley measures approximately 61mm in diameter. Choosing a genuine OEM idler pulley guarantees factory-specified bearing tolerances and material quality for quiet, vibration-free operation and a long service life.