Timing tensioner provides appropriate tension and absorbs the vibration of the Timing chain. These are part of Timing kit.  Idler Pulleys are responsible for leading, changing direction and tensioning the engine drive belt and ensures the belts do not collide with each other. The first sign of wear is squealing noise when  the engine is running and the parts needs to be replaced. Check our online car engine parts store to buy best quality aftermarket parts and Top brands like Gates & INA Timing Tensioners. In case of any query do get in touch with us.