PLEASE HELP!! P0446 and Gas

[ryan0413]

I've got a check engine light on and I read it with a tester and it showed P0446, I thought it was my gas cap for a while even though nothing seemed wrong with it. I've been told that this code can be anything from the gas cap to where the gas hits the engine. Tonight I was topping off my gas tank just a couple of gallons, and rather than stopping the gas starting spewing everywhere outside of the car. I've also been getting pretty poor gas mileage about 16-17mpg city. I've got a 1999 Solara, V6 with 123,228 miles, please help any suggestions will be greatly appreciated.

[Hajoca]

Vacuum switching valve on charcoal canister may be worn out.