Engine needs to do four basic things. Breath in, take in fuel, spark the fuel, breath out. Its more complicated than that, but basically the things associated to each that could cause your problem:
Breath in - Air Intake Severely blocked
Take in Fuel - fuel filter needs to be changed, fuel pump going.
Spark the fuel - Cap/Rotor, plugs, wires
Breath out - Catalytic Converter is broken up/blocked.
My bets are on fuel filter or cat converter. Get under the car, bang the catalytic converter solidly with your hand. If you get a lot of rattle like you poured broken glass into it...bingo!