the idler pulley on my '98 froze up and broke the belt. (Just got the Cherokee from a friend - It has been sitting for a few years).
The replacement from Auto Zone had a different sized sleeve that sits inside the bearing. It was too small, so I tried to reuse the old one. When I put it on, the pulley rubs against the mounting bracket. Is there some sort of spacer that goes between the pulley and the back?

 

i had to replace mine aswell and when i went to advance auto parts to get one they had 2 listing... so i got both one fit like your saying yours did and the other fit perfect. so there is a chance your in the same boat and they gave you the wrong one. check it out

 

I went to the junkyard and took one apart. Sure enough, there is a spacer that goes behind the pulley. The auto parts store didn't have any reference for that part. Up and running.

 

Yup, was about to say. It has a spacer.