revs to about 3000 ? if it was around 2800 or 2900 i would be thinking its going into limp mode
exactly what mine was doing (faulty AFM) so i ditched ecu and bought a vi-pec ecu so i dont need afm's anymore
cheaper option for you would be to try a afm off a mates car and see if that fixes it then you know to go and buy a new afm