Hi, i bought my 05 roadster yesterday and it was having the same problem...i changed the crankshaft positioning sensor and it didnt solve the problem, then when i open the trunk i saw a little hole in the trunk, on the back of the seats, which had some kind of pump in it....it was wet probably due to rain(it is convertible). I dried the cables and the isolation with a hair dryer and the car is working perfect again, i hope it helps...