Did you adjust the tension of the belt? It sounds to me like you pulled the idler pulley off, put a new belt on, and then tried to put the pulley back on? Hell yes that would be a pain to say the least! What motor do you have? On the 4.0 motor, you adjust the belt tension by loosening the power steering bracket and backing off the long bolt under the pump. Once that is loose, you can swap your belt and tighten back up.
Not sure when they changed to a tensioner, but in the pic above it looks like the idler is not moving, but the pulley above is. If it has a tensioner then he should replace the idler, or adjust the belt if he doesn't have a tensioner.
I wish mine had the tensioner, it's kind of a pain to adjust the belt.
Thank you for mentioning the Spacer, I found it on the ground. (on the left , photo 1). I would still be scratching my head .
The tensioner (photo 2) would be that long screw. So I think technically I wasnt supposed to actually remove the pulley, I would just need to untighten its screw then turn the tensioner screw that will move the whole pulley up and down as needed.
It sounds too good to work though.
So now the job is done, no more burning rubber smell. There was a funny squealing that would increase volume as I increase the RPM. So I simply untightened the belt a little bit , using the tensioner!