The door opens at takeoff power as I see the light blink on (when the switch is set properly) for a second or three.

If the alternate air door is opening at full power, there are only two possibilities:

1) The spring on the door is too weak (very unlikely).

2) The K&N filter is not adequate.  VERY likely, as I found the same problem with my IO-550 in my Bonanza when I attempted to use the K&N filter.

I have removed the K&N filter.

Buyer beware.

Walter Atkinson
Advanced Pilot Seminars