If your accessory belt idler pulley is starting to show signs of excessive wear, such as wobbling, grinding or squealing caused by a failing bearing, the idler pulley needs to be replaced before it fails and leads to failure of the belt itself.If you are replacing your accessory belt idler pulley, now would be a great time to inspect and replace other components in the belt drive system, such as the tensioner or the belt, it they are starting to show signs of wear. ECS Tuning carries a full line of belts, tensioners, pulley and the associated hardware you need to keep the belt drive system on your BMW functioning flawlessly.