If you can stand any more advice - why don't youleave it with the dealer to have them drive home until it screws up? They should be able to provide you with a loaner, which gives them added incentive to find the problem. I used to be a service advisor at a VW/Porsche/Audi ddealership and have used this technique. It's the only way to solve intermittant problems! If only cars were as cheap and plentiful as advice!