Fuel problem

I've got a 2000 Jetta with a 2.0 and 5 speed. The car will not start after I put gas in it, unless I hold the accelerator to the floor. The car starts fine any other time, but after after putting any amount of gas ( fill it up, or half a tank ) it will not start on it's own. I've tried taking the gas cap on and off without putting gas in it, and it starts OK.

Any ideas ? My local VW dealer can't figure it out.

I'd have them check the fuel EVAP system (tank vapor control system) and the purge valve. It sounds like fuel is backing up into this system & flooding the engine.