I need serious help w/ my Cavalier

1996 Chevy Cavalier, 171,000 miles, 2.2 L.
I have a few problems linked to one. My car sometimes will start then the next time I crank it, I will have to give it gas then it wont do anything because the #1 or #4 cylinder gets filled w/ fuel & I have to pull the spark plugs out & spin the engine over put them back in and then it will start. And here recently it has started back firing and skipping bad. This problem keeps occuring. I have replaced plugs, wires, injector, tps sensor, both coils, ignition module, map sensor, egr valve, and fuel pressure regulator. The only other things I have recently had done are thermostat, transmission, temperature sending unit and a radiator. My mechanic hooked it to a snap on scanner and it gave code po300 which said random cylinder misfire. Please help my mechanic is sucking me dry! :(