Hmmm... not sure which one you're referring to as there are two belts and multiple pulleys. I will say this though. On the outermost belt (the fan belt), there are no "idler pulleys", only a tensioner, the crankshaft pulley, and the fan pulley. On the inner belt, there is both a tensioner pulley (located more on the driver's side) and an idler pulley (located more on the passenger side). The easiest way to tell the difference is that an idler pulley is always just that... a pulley. The tensioner always has some "lever" or some way to adjust or relieve the tension and is usually off center from the bolt. As far as the width of the pulley, I don't think that should be any different, but I believe I have heard that replacement idler pulleys for the LR3 now come with an outer lip to prevent the belt from sliding around.
At any rate, the manual here may help. Just click on "Description and Operation" to see the different pulleys.
At any rate, the manual here may help. Just click on "Description and Operation" to see the different pulleys.
