Most common peformance problems on Turbos,
MAF meters either because its getting dirty from a very dirty Air Filter or its faulty, usally due to age. Either way its best or you will have to change it.

The car could also be overdue fo a spark plug change, if you drive the car very hard you must do a major service at around 12 000Km were they will chnage the plugs.

The best is to just take the car to a Porsche Center were they can diagnose the peformance problem with the car.