Does anyone know why on autopilot the throttle is going crazy and going up and down erratically?
I guess it’s trying to maintain a constant speed when the wind conditions are not very favourable.
Are you going too fast. Sometimes it’s the wind, but I would try fly with spoilers if you are flying to fast. That would be my best bet (it works for me).
Also, use spoilers while flying fast? You shouldn’t be flying above Mach 0.85 in anything except 747.
This happens in real life as well when winds are quite severe and so the throttle tried to maintain the speed.
As @Flight_Gamer said, the auto pilot is trying to maintain the speed you have selected. :)