it could be your head gasket
Fuel going into the air cleaner could be a stuck float or improper timing, or internal engine problems. If the engine is also backfiring then the timing is probably off.
your float could be stuck
I dont think you have to worry about that. 1999 has timing chain I dont think you have to worry about that. 1999 has timing chain I dont think you have to worry about that. 1999 has timing chain it does have a timing chain but if it has really high mileage its better to check and replace if it needs it because if it skips timing it could seriously damage the motor
Could be low on coolant.
One reason a 1993 Chevy Lumina may turn over but not start could be the battery. It may also be the spark plugs.
check neutral safety switch, or it is possible that a bad ignition switch could cause this...or loose or broken wiring!!
there is a short some where in the electrical system... or a bad battery.
could be a bad TPS throttle position sensor OR a bad IAT idle air control temp sensor.
Could be a broken timing belt or a bad Engine Control Module.
Not overly familiar with the Lumina, but you might have accidentaly disconected them at the bus, or the CD player could be drawing to much power(unlikely)
could be your alternator