Also check the rubber intake boots for tears.
Especially the lower one.
There are I believe also some rubber caps that cap off some extra inlets for vacuum hoses at the back of the manifold that tend to disintergrate.
This indeed looks like a vacuum leak somewhere.
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Z4 3.0i | ESS TS2+ supercharger | Quaife ATB LSD | Brembo/BMW performance BBK front/rear | Schrick FI cams | Schmiedmann headers+cats | Powerflex/strongflex PU bushings | Vibra-technics engine mounts | H&R anti rollbars | KW V3 coilovers/KW camber plates | Sachs race engineering clutch | tons of custom sh#t
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