Car is hard to start and when it does it idles very rough. Pressing the gas pedal cause the car to stall and when it cuts off a thick cloud of white smoke blows out of exhaust. This all started after getting gas. I pulled out of the gas station and my car felt like it cut off. i pulled into median and realized my car had not cut off but idleing very low. Every since i got my car home the other problems started. please help!!