If that's about six inches in diameter, that's the charcoal canister. Fumes that vaporize mainly in the fuel tank on warm days travel to that canister and are stored there. When the engine is running, those fumes are drawn out and burned in the engine.

About the only thing that ever goes wrong with them is if they are cracked in a crash or the vacuum hoses become deteriorated and crack or fall off. Leaks in those hoses are monitored very closely on '96 and newer models. While those leaks are fairly rare, at the worst if a hose is leaking you might smell fuel if you stick your nose close to it.

Answered by caradiodoc (expert)
17,643 answers provided

Thanks for the prompt reply. On a side note, is it normal for a clicking sound to be coming from it? Im curious because Ive been having problems with the vehicle surging when idling and trying to diagnose potential problems. Tonight i opened the hood and heard a very audible clicking from the canister. Also the hoses are pretty worn and cracked.
Thanks again!

Response from mrbeauman3
6 questions asked

The clicking is a solenoid that cycles on and off to vary the average flow rate of the stored fumes to prevent an overly rich mixture. Many cars have that solenoid mounted right on the engine and you can hear it from inside the car with the windows rolled up. On most cars it never cycles on until you reach highway speed. That way it's not noticeable as far as sound or engine performance.

Answered by caradiodoc (expert)
17,643 answers provided