Ok so im only 17 and dont know a whole lot about cars. What i do know my family doesnt believe because well, im 17. Anyway i noticed after i got my exhaust put on that the puffs of air coming out of the exhaust arent nice and even really uneven. Its not missing its just running oddly. Also the air smells heavily of gas. My dad seems to think it needs to go to the shop. I think its just the o2 sensor or the plugs. Any help would be greatly appreciated.