What else could it be?

My Taurus has been run for diagnostics, it showed the oxygen sensor, crank shaft position sensor, misfire on the 1 and 4 cylinders. I have put new plugs, new fuel filter, crank shaft position sensor on it, the old fuel filter was dirty, the catalytic converter when you mashed on the accelerator would give off an odor of rotten eggs. When you try to accelerate, the motor lugs down and the maximum speed is about 20 mph.
When we took the cover off the air filter, you could hear a gurgling sound like it was starving for air.