Increased rough idling, loss of power.

Increased rough idling, loss of power, squealing noise on acceleration especially hard accelerations, gas smell, and poorer gas mileage. Have replaced the knock sensor since the obd code said it was an engine knock or bad knock sensor. The check engine light went off, but still is experiening the above problems. I have done some research and some symptoms point to either a bad catalytic converter or bad air flow/fuel sensor. Any ideas on what might be going on. I plan on changing the plugs and fuel filter also.