vacuum connections at the brake booster and clearly showing the vacuum one-way valve (blue)
This is the flappy control relay that actually connects the vacuum supply to the flappy. It shows the line to the flappy plugged, probably because of a leak under the intake. A vacuum line to the flappy actuator should be connected there.
vacuum distribution point at rear of the engine.
VACUUM LINE DIAGRAMS S3.pdf
The 4 way fed from the brake booster has 4 connections:
- vacuum feed from brake booster via check valve
- vacuum feed to hvac manifold
- vacuum feed to flappy valve solenoid switch
- vacuum feed to vacuum accumulator (egg box thing behind the wheel well)
This tool will help a lot finding vacuum leaks. Porsche P9160, Mityvac is the supplier.