Audi Coupé 20V 7A no power

Servus, Have an Audi Coupé 20V 7A Built 89 with 170hp. The car doesn’t really have power and the infamous thrust is missing at 4000… Sometimes he has a slight jerk between 2000 and 3000. Have already read out the error memory, but he says 4444, i.e. no error is present… Intake hose is also new… I checked it on false air and found nothing… Do you have any tips for me? Thanks already… mfg