92 cavalier, fuel pumping thru vapor cannister vent

My sons 92 cavalier has rough idle and sometimes dies once operating temp is achieved. Fuel is flowing out of the vapor cannister vent port when this happens. Any suggestions?

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Which engine? 2.2 or 3.1?

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2.2 throttle body
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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. http://users.eastlink.ca/~smackie/evap.pdf
If it all checks out, it may be further up the line. For that, I'll have to do more reading.
Steve

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thanks for the info. I'll give this try tomorow.
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Overfilling the gas tank by forcing as much fuel in as possible can cause fuel to be forced back in the canister as the cool fuel expands....

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