I am making a panel for the embraer 170 by dreamwing, and have made all the gauge using XML, The problem I have is the autothrottles. When autopilot is set for 250 or lower the throttles rev up and down.I have no idea what is causing this problem so any help would be greatfully received.

Overshoot it is called. Caused by an over-sensitive controller. An expert in the controller business would be able to say "Aha, the proportinal factor is too high" or something along those lines. Sadly I am no expert... :-( I only know you may be able to fix this in the aircraft.cfg in the section entitled[autopilot]Scroll to the entrymax_throttle_rate=0.10and play with this value, particularly reducing it. The AircraftContainerSDKFS2004.doc states:"This value sets the maximum rate at which the autothrottle will move the throttle position. In the example, the maximum rate is set to 10% of the total throttle range per second. "