I noticed the other day that a component (breather valve) was not fitted properly (the clip that held the valve cover breather in place was sitting between the O-ring and the lip, instead of fastening the component to the top of the engine) and since have been trying to learn more about the PCV system in my car.

When I removed the valve I saw that there was a fair amount of oil in the pipe running from the air intake.

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I believe this is a no-return valve, and my first thought is that it is meant to allow the clean air to flow into the intake manifold along with the blow-by when the pressure above the valves/in the crankcase is low enough, but prevent blow-by from entering the air intake when it is high.

Alternatively, there is the (very high) possibility I've misunderstood the PCV system in this car and in fact that valve is the channel through which the blow-by enters the intake manifold in which case it would be expected that it was filled with oil.

enter image description here

  • Have I understood the PCV system correctly?
  • Should there be oil in my air intake?

The car is a 2002 Audi A4 2.0l (B6 body, no FSI).

3 Answers 3


Whether or not it's right for your car, I can't say as I don't know anything about Audis. However, it's normal for there to be some (not a lot) oil in the intake of the cars I'm familiar with.

  • 1
    Thank you, I think this is true of my car also. My concern was the quantity of oil and the fact that I thought the breather valve was not operating correctly. Today a week after refitting the valve, I checked the air filter and saw no sign of oil, and amounts in the hose had decreased. I also spent more time attempting to figure out the operation of the valve by blowing into its various ports and it appears it is operating correctly, with all ports allowing air to flow into the 'suction' port but not back into the intake.
    – sebf
    Oct 27, 2012 at 11:39

I'm curious to what you found by blowing into the valve. I recently replaced the crankcase vent tube which attaches to this valve. Upon disassembly, I cleaned out the oil gunk from the valve, but was able to blow into every hole with no issue. I'm assuming there should be some sort of diaphram in there, but not so on mine. What can you tell me from your experience?

  • 2
    There is definitely a diaphram in mine. When I first 'tested' it I sucked on the various ports (don't ask what possessed me to do that!) and, for obvious reasons, did not keep this up long. The second time I blew into the ports while blocking the others in various configurations to see where it directed the air and it was into the suction port. At the air intake end, there should be a grill/spokes like part, which the diaphram (which in mine is orange) sits against, anchored with a bit of plastic in the centre.
    – sebf
    Jan 2, 2013 at 16:06
  • (PS. The part No. (06B 103 235 G) is on this thread: uk-audis.net/topic/1597-a6-c5-vacuum-stuff)
    – sebf
    Jan 2, 2013 at 16:11
  • Instead of sucking on the hoses, they make really nice, not too expensive vacuum pumps with gauges on them. :-) Apr 24, 2014 at 12:47

Mine 2001 A4B6 2.0 NA , hasnt got that 'vacuum booster..' dunno why. But if any one part of the CVS is broken, I'd replace the whole lot of it. If its done 200,000kms its not a big ask from the car. Since you need to remove the alternator to get the bottom CVS housing iut ( cut it in 1/2 before removing) i'd also replace the complete cooling system, the rear flange & electric thermostat& hoses, since the alternators out. Its all the same plastic & breaks down at the same time. Not idling properly = CV System. Runs cold all of the time = thermostat. A days easy job on. Non turbo. 1/2 day if you have done it before. All the 'O' rings will be damaged expressly the rear coolant flanges, the inner ring crumbles & the O ring slips inwards & the thermostat housing breaks inside & the thermostat comes loose. You will never have to touch it again either.

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