Car came in with cam crank correlation codes and flap position fault. cam and crank code solved but flap position still logging.

The flaps open at the correct time (above 3000rpm) but fail to return as requested buy the vehicle. Thoughts were sticking flaps, however as soon as vacuum supply to the control plunger is removed (by disconnecting hose) the plunger returns.
It seems that the vehicle is not evacuating the vacuum supplied to the plunger but I see no way that it can? the control solenoid is brand new from TPS.

Have spoken to Auto logic and they are stumped and basically said throw a manifold at it which I can understand given rate of failure however the problem seems to be with the vacuum control, from what I can see but everything in the system 'appears' to be operational??

What am I missing??

Regards

Luke Browne