I think I might have a bad tensioner on my 99 Dodge Caravan and I need to know how to go about replacing it. I have had to replace my serpentine belt because it keeps popping off when it rains. I noticed that when I'm looking at the belt as it runs across the tensioner pulley it slides back and forth across the face of the pulley but not to the point where it comes off. Do I need to replace the tensioner, pulley, or both? And if so how do I go about doing this?