http://www.amazon.com/gp/aw/d/B004IYZLIU/ref=redir_mdp_mobile/184-6831769-0176309?creative=395097&creativeASIN=B004IYZLIU&linkCode=asn&ref_=asc_df_B004IYZLIU2853084&smid=ATVPDKIKX0DER&tag=pg-95-94-20 This is the vapor canister vent valve that a buddy of mine replaced on his Subaru when his did this. I'm not sure that's your problem, but he said it probably is. This might not be the right part for your car specifically, so if your buying one make sure you look it up first. Good luck!
Write up I found about it also-