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I still haven't fixed it but I have a question. When I stop/park my car, there is a vibration emanating from my gas cap. I assume it's "passing gas". Is this normal or could this be the source of the check engine light? I made sure the cap was tight and it still "farts"


No it is not normal.. Your gas cap is leaking.. It's actually pulling air in, not leaking out as engine manifold vacuum is used to pull a partial vacuum on the gas tank for emissions reasons.. You probably have error code PO440 set which is defined as follows:


Per the Factory Service Manual...
PO440 will be set when the fuel tank pressure is atmospheric pressure after the vehicle has been driven for 20 minutes.. (meaning air is leaking in and the system can't pull a vacuum on the tank..

Possible Trouble Areas:

Hose or tube cracked, holed, damaged or loose seal.
Fuel tank cap incorrectly installed
Fuel tank cap cracked or damaged.
Fuel tank cracked, holed or damaged.
Charcoal canister cracked, holed or damaged
Vapor pressure sensor
ECM

2000 4Runner,V6,Auto,31's, Sliders, Skids, On-Board Air, Air Shocks
Related Interests: Welding, Ham Radio, Road Tripping (Blue Highways), High End Video/Audio Systems