I have tried two different serpentine idlers, they seem to have a slight but noticeable 'knock-knock' with rpm changes. Even at idle it looks like the idler is 'bouncing',,, tried different belt also. Does this mean one of the other pulleys is out of whack,,,, which is causing the idler to be bouncy instead of smoother tension ??? I am sure both idlers were on low end for price,,,,, but will a high priced GM idler act differently ??? 2000, 3.4L .

 

Watch all the pulleys while it is running to see if one of them wobbles and if they are all in line with each other. Is it a new idler?

 

yes, two new idlers, both 'knock' after a short time,,,,,they were low dollar idlers,, also tried a different belt,,,,,,,,,,,,,, my grandson works at a parts store, so he is getting a new idler, Dorman brand,,, will inspect belt and pulleys, look for any flaws,,,,,,,even when not knocking, the idler seems to move or bounce a lot ,,,,,,,,,,,

 

to clarify, you are talking about idlers not the tensioner or idler pulleys on the tensioner

 

serpentine tensioner, idler tensioner, this is what knocks after two replacements,,,,,, it has a bounce to it, then after a short time, it has a
slight knock,,,

 

dorman is crap also. buy a oem from the dealer.