[Brian R.]

Possible Problems
Fuel tank cap incorrectly installed - loose <= Most common
Fuel tank cap cracked or damaged (Use Toyota part only)
Bad vapor pressure sensor/circuit
Vacuum hose cracked, holed, blocked, damaged or disconnected
Hose or tube cracked, holed, damaged, or loose
Fuel tank/filler neck cracked, holed, or damaged
Charcoal canister cracked, holed, or damaged (collision)

In above description, check hoses between vapor pressure sensor and VSV for vapor pressure sensor and charcoal canister. Also, check the hose between charcoal canister and fuel tank.