2003 Volkswagen Jetta TDI 4 Cyl 1.90L
why is the accessory belt tentioner vibrating ?
replaced it, replaced belt, cleaned pulleys, still does it what is next,
Check the belt alignment - follow the belt routing over all the drive pulleys where it makes contact - insure the belt is routed and mounted correctly. Next, be sure the tensioner is properly mounted and tightened securely, and the tensioner engaged with proper tension on the belt. Then, check the other belt-driven components; the alternator, water pump - to be sure these bearings and pulleys are secure (not loose or worn). Finally, be sure you have the correct belt part number (length) for your application. Try the many on-line auto parts sources, such as; www.RockAuto.com or www.autopartswarehouse.com for the replacement part.