I think you are talking about anti shudder valve. It only has two positions open and closed, it does not participate in airflow regulation, just cuts air supply when you turn ignition off so that you have smoother engine stop as it does not have to compress air in cylinders. Added benefit is that it eliminates possible engine run away.
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Currently 8less
2011 Q7 S Line 3.0TDI, 2016 Tesla Model S 90D
8 history:
2006 A8 Sport 4.2TDI quattro SOLD,
1997 S8, reached end of life with gearbox failure
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