I have a PD 130 AWX and when its been cold overnight the car has the same symptoms as you have for the first couple of seconds. Something i'd like to sort also. My thoughts have always been that the injectors need cleaning. I also have an old shape S3 and the others on that forum swear by removing the injectors an using an ultrasonic cleaner to clean them.
Link here..
Postal cleaning service
Link here..
Postal cleaning service