I own a 2002 Dodge Neon SE, Automatic Transmission. The car seems to run well except for the occasional low idleing (feels as though the car needs an oil change but recently had one). The SES Light came on and reads error codes:
P0420 Catalyst Efficiency Below Normal (Bank 1)
P0442 Evaporative Emission System Leak Detected (small leak)
P0455 EVAP Large Leak Detected
Any Suggestions on what this all means and where I can start looking for solutions. Thanks.

check to make sure yer gas tank cap is on tight...or possibly try a different gas cap as that is the usual reason for the small leak sometimes large leak as well.

Cat might be clogged or broken or exhaust might have a leak somewhere... thats for the first code... your gas cap might be shot... time to buy a new one

I know it's not the Gas cap as I have already tried that and bought a new one.

well if both gas caps were aftermarket then that could be yer problem ... u get the gas caps from the dealership or somewhere like autozone?

It's most likely the lines near the gas tank...