My 2010 XC90 accelerates poorly in warm weather and is fine in cool weather. Possible sensor or throttle actuator? Wisdom appreciated!

 

could be a temp sensor or an intake air preheater mechanism not working correctly. Not sure how the throttle actuator would behave differently by ambient temperature.

 

Depends what you mean by "poorly"? Any turbo charged engine will have diminished performance as ambient temperature goes up; nature of the beast.

But if it's actually misfiring or something like that, then you may have a real issue.