The coilpack delivers the electical charge to your spark plug.
Yes there is a slight flat spot on a standard S3 about 4000rpm before it picks up again.
Diverter Valve (DV) - If this goes u will know about it, i was informed i prolly wouldnt get out of 3rd if it went.
Coilpack - Again u will know if one of these go the car will only be running on 3 cylinders if one goes so it will be running real ruff and u will know there is something wrong.
Air Intake Hose - Flat spot about 5000rpm could be your air intake hose collasping but it is usally a problem with chipped cars (is your car chipped).
Wastegate - I currently have a problem with my car its got a flat spot about 2500rpm and then it picks up about 3500rpm but not properly, it has been diagnosed as the wastegate is sticking.
Mass Air Sensor - Not to sure of the symptoms.
But i would say the Air intake hose if it is chipped.
Are u getting a fault warning light coming on.