Air Oil Separator
The engine oil air separator directly affects the engine crankcase atmosphere because for the most part all Porsches from 1980 on including the current 986-987-996-997-Cayman & Cayenne engines all use positive crankcase type systems. The engine crankcase has vacuum supplied from the intake manifold to collect and burn the residual combustion by-products or blow-by in the crankcase by running it through the engine (intake) again, to lower the overall vehicle emissions. When the AOS fails you can usually see oil being burnt via smoke coming out of the exhaust. Inspection will usually yield a high crankcase vacuum (hard to remove oil cap with engine running) and oil pooled in the throttle body (intake).