CODES PO442 & PO446

2001 Toyota 4Runner

Engine Mechanical problem
2001 Toyota 4Runner 6 cyl Two Wheel Drive Automatic 156000 miles

I see these codes are related to an emission leak and control circuit malfunction. I ran 2 bottles of engine cleaner - the kind Advanced Auto recommended, not the $1.99 stuff - and changed the gas cap. The dealer says I need a need Charcoal Canister. Does this sound right? Gas mileage is starting to decline.
July 14, 2008.

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