yes the valve will close and stay closed I just wish i knew the name of the part either the valve or the actuator so I could do a search of the forums, i had an 87 300d as well but I do not remember how the turbo was set up on that car. The valve would close and cut the air supply to the intake and this is why the engine would stop, and it would take about 30 sec for the vaccuum to build which closes the valve . I am curious as to how that actuator works under normal cicumstances. When would it close this valve of partially close it .