check ignition
lack of fuel
dirty carb bowl or water in the carb
you can but it wont stay running if the battery is dead
have a pontiac 6000 2.5 motor and it wont stay running
Check the idle sensor if you have one.
bad alternator, dead battery.
The Optispark distributor is notorious for causing this problem.
Type your answer here... It could possibly be the ignition switch.
Check the fuel pressure on the Fiero to start with. It sounds like it could be starving for fuel.
Start by checking your fuel filter.
dd