Or, Purge Valve For Fuel Vapor Canister, depending on where you look.
Appears to fit 97-04 Boxsters with OBDII emissions.
I pulled this out of my car when I thought it was a problem. But, it wasn't. So I replaced a good working $117 component...
This is the original part, marked 99T028. Since there's risk involved with an older part, I'll sell it for $15 shipped. PayPal or send me a check.
This is the valve that sits at the top of the charcoal (EVAP) canister. It also fits somewhere else in the fuel filler neck, if I recall correctly.
This valve pictured is the new valve I received. The one I'm selling is the one that came out of the car when I put this one in. Photo is just so you can see what the valve looks like.