Use a "straight edge" to make sure that the "valley" area (where the belt rides) is in alignment with the other pulleys
If it does not drive anything it could be an idler pulley.
i dont really know-but to find out just look it up on google!
Need to know if you have a Detroit, Cat, or Cummins engine in order to answer this. As for the idler pulley itself, it's pretty simple to locate - it's the pulley which only spins, and doesn't actuate a pump, alternator, compressor, etc. Removing it is as simple as loosening the belt, unbolting it, and installing it in the opposite order.
The marks are located on the Cam Shaft Pulley... should be easy to spot... make sure that you have the proper timing light, and do your reserach so that you will know exactly how to time the vehicle... putting it at TDC and linning up the Cam Shaft Pulley.
Remove belt and check to see that it rotates freely and smoothly
there is not a specific torque for the idler pully. tighten it up with a ratchet and it will not loosen up
Normally the idler wheel will have a bad bearing and will make a lot of grinding noise and or vibrate big time! If the bearings go out all together you will know real quick like as it will most likely burn or rip the belt off!
According to Troy Dean Potensky's Auto Parts in Issaquah, Washington, you may have to see a professional for that if you know what I am saying ;)
the pulley is bad when it stops moving
No, not that I know of. ZXTuner sells an AC Delete pulley that replaces the compresser with an idler pulley. I have it on two of my ZX2s and it works fine and is easy to install and no new belts are required.
Probably the idler pulley or the tensioner pulley on the serpentine belt. Carefully use a little squirt bottle and spray each one with a little water. When it gets quiet you know which one to change.
There is an available bypass kit, but the belt is the same. You remove the ac compressor and install an idler pulley.