Raven wrote on Oct 21^st, 2009 at 4:01am:

As for engines this may happen if you fly in real weather and the wind is unstable and changes direction, though I never use autothrottle below 10000.

It is not the wind. I experienced this autothrottle speed hunting issue even on a no-wind flight. The autothrottle speed hunting behaviour happens, for instance, on leveled flight during autopilot heading turns. For example, I am flying with autothrottle ON and VNAV or ALT HLD, leveled at cruise altitute (i.e. FL370, FL240, 12000, etc.) heading 360 on HDG SEL... change the heading selection to, say, heading 260 and right-click the HDG SEL knob to begin the A/P heading turn from 360 to 260... See what happens? Not only does this aircraft engines start to rev up and down to try and maintain the autothrottle speed, it also becomes somewhat unstable trying to climb and descend to maintain the A/P altitude during the turn. None of my other payware aircraft do that.