An idler does not transmit power but helps to guide or tension a rope or a belt. Usually, the belt runs through a guide pulley which in fact does transmit power and its direction. In most vehicles, the pulleys are used as part of the engine drive system and also to drive the fan belt. However, many modern vehicles also use a series of pulleys for the air-conditioning and current delivery system. That said the function and size of the parts change depending on what they are being used for which is why it’s important to buy the right guide pulley to replace a faulty one.
The most common problem is a loss of power, squeaking, incorrect tensioning and the belt constantly breaking. If you experience any of these issues its best to take the car to a mechanic. The mechanic will then determine if the idler needs to be changed or if also the guide pulley needs to be replaced. However, it's rare for both to be replaced because its only either one that’s causing problems. That said replacing either of these parts requires a professional and shouldn’t be done without experience as incorrect installation can cause damage to the vehicle.
As mentioned above the size and type of idler and the guide pulley will vary. So, the best way is to search our website via part number. At car-parts.ie we also offer discounted prices off every purchase of spares.