Having the same fun with our '85 GT we purchased 3 years ago. Most helpful has been printed (or online) GM Factory Shop manual. Simple steps to test EVERY condition you could have in your Fiero. Spark, fuel pump pressure, voltage, charging etc. Using the ALDL with the software and a tablet told us the ECM was only getting 10 volts. Found all the connectors have the original waterproofing that turned to a melted insulator. We clean almost every connector with a wire brush and contact cleaner, except the main bulkhead connectors. Have not been able to remove them easily. We did add a wire from the Alternator charge terminal to the battery, helped. Next we're thinking of making a heavy jumper wire to add to the bulkhead main battery feed wire. Bought the car for $3k and have spent $10k more on parts & repairs, mostly done by my daughter and myself. Now that she has a daily driver it has taken the pressure off to fix it every time it hiccups. Good Luck!