Please refer to this recent thread.
http://forums.pelicanparts.com/porsche-911-technical-forum/1118204-techron-fuel-systems-cleaner-good-something-else-going.html
The Porsche factory standard response to a Porsche running poorly was a bottle of Techron which is a Chevron Oil Co. product that can be purchased in most auto parts stores. If it was used at the Porsche dealerships, it must be good. I also recommend using it every few months.