What? Do you have an evap leak?

Very common spot would be the n80 valve (purge valve) With the engine off, remove the vacuum hose from it, get a vacuum gauge and apply 25 inhg of vacuum to it. It should hold vacuum, if it doesn't the valve is faulty.

Also, you should do what us VW technicians call a "paper test". Get a clean white piece of paper, bang the n80 valve down against the paper with the EVAP hose side facing downwards. Give it a few bangs, if black powder or charcoal comes out, you will have to replace the charcoal canister as well.