Just an FYI - I had my engine (with a Varioram on it) start idling very fast (1600-1800 RPM). I t took me a while to figure out what was going on and what failed.
The cause ended up being a failed check valve in the bundle of spaghetti hoses on the driver front side of engine. The check valve was allowing air to flow freely into the engine. There is an aluminum pipe from the fresh air side of the butterflies that ties into the spaghetti hoses and this becomes the source of air if the check valve fails. There are 2 hoses on the top side that link to the manifold after the butterflies that are the intake source of the air. The check valves are tied in with crimped clips which have to be removed to pull out the various valves to check for function.
Anyway, just thought I would share, as it had me talking to myself for a couple of days.

Bill -THANKS-Great information. Since I have a 964 w a 993 Varioram the system is much simpler. But, is great to know how all the lines run.
Wonder how the spaghetti hose set up works ( on left rear, as you look at ). There are numerous valves that must work under different conditions. As the open intake (aluminum tube pre butterflies) must close down at a point to allow vacuum to work but not allow free air in to intake after butterflies.
Great Info