I changed to the 0,5mm nozzle and rised the current of the stepper to 0,75A.
Retraction is now 5mm/s, 0,5mm.
That works very good.
But I need to rework the airbrush nozzles. The filament will not come out straight.
Direct after extrution the filament bends upwards. This happens with the 0,3mm nozzle as well as with the 0,5mm one.