I just found out that a normal OBD=II scanner will not pick up certain Porsche codes, you will need a Durametric diagnostic tool for Porsches.
http://www.durametric.com/default.aspx Either take it to a Porsche shop that has one or you can buy a PC laptop kit with cable for ~$300 or so. I use to have one for my 997 to clear codes and stuff but sold it. Really nice tool only for Porsche. I would not let a mechanic start replacing everything and running a ~$3k bill by trial and error, it gets expensive and you're still not sure if it fixed your problem.
See this thread:
http://986forum.com/forums/general-discussions/46423-my-car-stalling.html