Hello. I've got a 2010 Honda Civic. It drives normal sometimes then other times it'll start to rough idle and when trying to take off it's very jerky/shudder unless you ease into the gas. If I'm on a hill and it's been acting up it's then very shudder like to get up the hill. One day I had 1 gas bar showing and it wouldn't start until I put gas in with a gas can ( never happened before) When it's driving funky I'm smelling a gas smell. A hand scanner is showing P0420.

Any ideas? Thanks