I know this sounds like a stupid question but does the MIL work? It should come on when you turn the key to the on position. If it doesn't work the bulb could have burned out. Take the car to Autozone or Oriellys and have them scan for codes.
If your MIL does work I doubt you have a bad cat, because it would set the code P0420 for sure, and possibly the code P0300. Also when the car is doing its surging the MIL would flash at you.
Fuel filter could cause this problem and not set a the MIL, but when mine was plugged I got a flashing MIL, and the car would just fall flat on its face. Its a $12 part, so changing it won't hurt anything.