The EGR tube on the Fiero V6 is notorious for cracking. If the engine doesn't stall with your finger covering the IAC port (and throttle closed), you've got a vacuum leak... and/or possibly someone has messed with the idle stop screw. (There should be a "plug" covering/hiding the head of this screw.) To take the idle stop screw out of the equation, cover the entire opening to the throttle body with the palm of your hand while the engine is running. If the engine still runs, there is definitely
a huge vacuum leak somewhere.
[This message has been edited by Patrick (edited 12-24-2021).]