I have just installed the dash8-400 on my new PC and the autothrottle does not work, you cannot even select it on the panel. I have resolved the problem, it is in the aircraft.cfg file, in the [Autopilot] section the line autothrottle_available is showing =0 it should be =1,this will allow you to select IAS, however it will still not work as the following lines in the [Autopilot] section need to be edited to read,
autothrottle_takeoff_ga=8
autothrottle_max_rpm=18000.0
At the moment the max_rpm is set to 90, if the .cfg file is edited to include these corrections all will work fine.