The wastegate flapper won't move easily if it's attached to the wastegate actuator. Release the actuator rod (mind the circlip) if you want to test the flapper. You can use the vent side of a MityVac to generate about 15 psi which is enough to get the actuator to open the wastegate.

If the turbo is off the car, do a visual inspection of the wastegate to ensure the wastegate valve hasn't disintegrated and it's centered over the wastegate port when closed.

Sixto
87 300D