This is an interesting problem so I'm trying to learn as much as I can about
the system right now.
I would suspect the canister is saturated with fuel. Maybe the purge
solenoid is not working, or there is a restricion in the vacuum line. Maybe
the valve is toast.
Here's the diagnostic flow chart for the purge valve.
If it all checks out, it may be further up the line. For that, I'll have to
do more reading.
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