The CFSA 4.2L V8 in the B8 RS models integrates four functions into essentially three hoses:
- positive crankcase vent - a pathway to allow positive pressure build up in the crankcase due to blow-by gasses to vent out. As these gases contain significant hydrocarbon content, they are routed to the intake manifold to be burned rather than vented to the atmosphere.
- negative crankcase pressure - a negative pressure crankcase provides for better ring seal, reducing oil consumption to the combustion chamber and reducing blow-by. Vacuum from the intake manifold is routed to the crankcase to establish the crankcase vacuum. As the intake manifold vacuum is much higher (20 inHg maybe) than desired in the crankcase (maybe 3 inHg), a pressure regulator valve is used. As it happens, the PCV function also uses a pathway from the intake manifold to the crankcase.
- fresh air breather - since there is a vacuum path now established, if we vent fresh air into the crankcase, we can always be pulling the water vapor logged crankcase gasses out of the crankcase, preventing the water vapor resettling into the oil on engine off. The CFSA does this by routing a line from the left air intake pipe (after the air filter) to the crankcase.
- crankcase gas oil separator - As the crankcase gasses are being burned off, we really don't want to lose the oil itself in the gasses. So oil separators are built into the cylinder heads. As such, the IM vacuum is routed to the cylinder heads, which have integrated oil separators, which route the vacuum to the crankcase.
https://audi.7zap.com/en/usa/audi+rs.../1/103-103030/
The fresh air breather path is just a pipe (item 3) from the left intake elbow pipe to the top of the block, to a plate next to the oil filter stand:
CFSA crankcase breather tube.jpg
The CFSA is a naturally aspirated engine. Everything is at ambient or vacuum. The air in the intake path is at ambient at most, the air in the engine bay is at ambient. All the having the hose hanging free from the intake elbow did was allow dirty engine bay ambient air into the engine, rather than air cleaned by the engine air filter. The CFSA is a MAP engine, not a MAF engine, so there's no air metering issue that would have been introduced.
The intake manifold vacuum path is a pair of pipes (items 1 and 2) with regulator valves, going from the intake manifold to each cylinder head. This is likely your problem area.
It's nice that ECS puts up nice pics of the actual products, but they do love to leave out important aspects. Notice the top of the regulator valve, there's one direction where it has a raised flat.
Now we can see the outside of that flat, it's a hole.
The regulator valve regulates the amount of vacuum from the intake manifold exposed to the crankcase (cylinder heads) by opening up or closing down the opening through it. There's a spring that holds it open, and ambient air pressure is filling the backside through that port. When the valve is filled with ambient pressure, the inside and outside pressure cancel and there's just the spring pressure holding the valve open. But when vacuum is presented, now the ambient pressure on the outside is no longer offset and now pushes down on the valve against the spring, closing it in accordance with the amount of vacuum present.
What you have most likely is a torn diaphragm. Now the balance act is broken, the valve opens fully, full IM vacuum is passing to the cylinder heads and crankcase, and the IM vacuum is likely pulling in air at a high rate through that little port. If your car sounds like a freight train whistle, that's your whistle.
The CFSA, as mentioned, is a MAP vehicle, so you won't get a rough idle per se, certainly not like my 2.0T, but you're still exposing the crankcase seals to extreme vacuum. More than one RMS has been blown by such conditions.
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