Mk4 tdi anti-shudder valve

Hoping someone might have a bit of experience with the Tdi engines in the mk4 golf (ALH engine code)
The anti-shudder valve hasn't been working for the last while and being off work at the moment I said I'd have a look at it!

From my understanding of the system a vaccum pulls the actuator which closes the flap stopping air entering the inlet manifold and reducing the violence of the engine shudder as it turns off!

I did some reading online about common faults and found that the two wires, small purple and yellow ones often chafe so I started looking at them! Both had signs of wear but had previously been protected with insulation tape so are ok!

I then disconnected the vaccum line the connects the anti-shudder valve to its solenoid, covered the outlet port on the solenoid with my finger and turned off the engine! I was able to feel the vaccum pull on my finger so I assume that part seems to be working! I reconnected the line and cable tied both ends to ensure no leaks but still the valve won't move when the engine is shut down! It does move freely by hand so it's not gunked up with carbon either!

That's as far as I've got, hopefully someone else here can guide me to the next step!