I had this happen once after I took apart my upper and lower intake. I put everything back together and the car was getting bad mileage on top of really strong gas smell. Ended up one of the fuel injectors hadn't seated properly in the lower intake manifold and was leaking small amounts of fuel over the top of the engine. I thank God I found the problem in a few days and I didnt start a fire. I took everything apart and reseated the injector- problem solved.