If the first test works then applying power to the solenoid should let the flap open when closed(activated with vaccuum and no power.) Your DISA is likely fine.
Butt connectors are likely a big part of your problem.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)