I drive a 1999 Toyota Camry, around 150K miles. The car is driven infrequently -- perhaps two or three times a week. I'm in the Southeastern US, where recently we've experienced mild but chilly weather (above freezing).
Anyway, around a month ago, I started to notice a gas smell when I start my car. It is brief, and only happens about 15-30 seconds after I start it. My driveway is a bit sloped, and something (a piece of plastic?) scrapes on the ground as I back out. Not sure if this is relevant.
To start with, I inspected my fuel tank cap and noticed that it was screwed on a bit funny, so I removed it and screwed it on again.
I also looked under the car and found no apparent fuel leakages or the like.
The next morning I again noticed the smell, so I took the car to a mechanic. They took a thorough look, removing the back seat so they could inspect the fuel tank, and found no leakages or other apparent problems. They speculated that maybe the fuel tank cap thing had fixed the problem, and told me to bring the car back if I noticed the smell again.
After that, usually the problem didn't occur, but on Wednesday I noticed the smell again.
So I took the car to the mechanic again, described all of the above to them, and asked them to take a careful look. They elevated the car, again looked at the fuel tank and found no leaks, and were unable to find any apparent cause or problem. She sent me home without any recommendation.
At this point, is there any way I could determine and fix the cause? And would continuing to drive it be a safety hazard?