Hi, need to replace the idler pulley in my 98 se. The old one broke, so I have no comparison. Auto Zone and Advance both show 2 parts for my car, one is 3 inches the other is 3 1/2 inches. Which one am I supposed to use? thanks

Take a look here. https://www.gmforum.com/mechanical-134/pulley-change-index-285990/ I believe your talking about pulley #3 That'* a 3" pulley

Just remembered, I have 2 of them in steel. $15 each shipped.

Thank you. Is that the same if its not supercharged?

Yes, both belts use the same idler. Both tensioners are 3"