thanks for the expaination, how should i clean 1 and 2 warm soapy water?Based on their appearance, 1 and 2 are cyclone separators. The oily air entering through hoses 14 and 15 comes in tangentially and swirls around inside like a vortex so that the heavier oil gets flung to the outside and drains down to hoses 9 and 10 back into the engine. The de-oiled air in the centre of the vortex escapes up through the top nozzle to the plenum. Unless BMW got fancy and installed internal check valves or similar, which should visible through the nozzles, I would just clean them well. Since cyclone separators depend on unobstructed drainage, I would also blow low-pressure air through the drain hoses to make site 9, 10 and 5 are not plugged.
+1 Brake cleaner should be great in cleaning these. Needless to say you have to remove them completely before ouichIn terms of cleaning, they're just plastic pipes that get oil gunk in them, so anything that would dissolve and clean that away would suffice. As per the answer above, they're not some of the pricier parts to replace and tend to have quite an effect on the way the car drives, depending on how gunky they've got. Symptoms of issues include oil in the plenum after lifting the top and oil visible in the air intakes, under the filters or near the MAFs. Lots of info historically on here on the oil seperators.
The bottom hoses are usually worse, as the bore is so much smaller. FWIW when i replaced my top hoses they weren't all that bad, but the bottom hoses had virtually collapsed in on themselves and were duly changed when the stat was doneI never replaced the bottom hoses either, I'd only swap them out if they are squishy really. The top hoses tend to get much worse.
+1 --- Spot-on!The bottom hoses are usually worse, as the bore is so much smaller. FWIW when i replaced my top
hoses they weren't all that bad, but the bottom hoses had virtually collapsed in on themselves and
were duly changed when the stat was done