2003 Ford Taurus Problem

Only had the car for 2 months (purchased from public auction) and everything was ok at first but 2wks after getting the car the service engine light came on so I took it to the dealership and they replaced my wires/plugs and the light went out 2days later and no problem until 3days ago. The car idles loud, shakes/tembles slightly (especially when im at a stop sign or red light), and I smell gas when I crank up. The car cranks fine, drives, accelerates and changes out just fine but I have not driven it since it started giving me these problems because Im not sure if I'll cause more damage if I do drive. Can you tell me whats goign on with the car?