Check the fuel pressure on the Fiero to start with. It sounds like it could be starving for fuel.
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
Check the idle sensor if you have one.
have a pontiac 6000 2.5 motor and it wont stay running
bad alternator, dead battery.
Bad starter motor?
The Optispark distributor is notorious for causing this problem.
Type your answer here... It could possibly be the ignition switch.
Mine wont start because the engine is out on the rebuild stand right now, Yours I have no idea
Start by checking your fuel filter.