P0299 under boost fault

[Passat_ben]

Okay guys, I've had my car in and out of garage many times now and it's still throwing the fault. I've had a leak on my inlet manifold repaired, I've had the vacuum solenoid replaced and now they cannot find a fault.

I've started checking things my self have found the turbo actuator seems to operate after maybe a 1-2 second delay after revving the engine. Once the revs start to die down, is this normal or should that be an identification of sticking veins or a fault with the actuator?

Also apparently there is no vacuum leaks however I'm dubious of that fact.

Any advice guys on what I could check and more importantly how?