Galant 2001 loses strength

I have a 2001 2.4 engine, mechanical, it is giving me the problem that comes out that it costs to match, I have to heat it at least 10 minutes before leaving but fixed problem, they told me that it was the thermos switch but I already changed it and remains the same. The fault it has is that suddenly a smell of gasoline begins to emanate and begins to faint and lose strength, turn it off a few minutes and then start working normally. What could be! ???