Identify this part!

[sleepingboxster]

Originally Posted by stelan

That part is part of the pcv
It is a spring loaded valve that prevents your seals to blow if too much pressure in the cranckcase is present.

If you have a semi operational AOS and bad spark plug tube seals the car leaks little oil if you disconnect or cap the throttle body to AOS hose the car with bad spark plug tube seals will leak a lot of oil because there is no vacuum present in the crancase and the pressure builds up and leaks like crazy.

You have, I believe a combination of the following:
A) bad spark plug tube seals AND
B) bad or going bad AOS diagragm (hissing)

Or
A) bad spark plug tube seals AND
B) vacuum leak

Vacuum leaks can be found at
-hose from drivers side vent valve to aos
-aos itself
-hose from aos to throttle body
-aos bottom bellow
-dipstick tube
-oil fill tube
-little hoses that go inserted into intake bellows
- little hose that connects to throttle body
- throttle body boots

Changing the spark plug tubes or/seals will stop the leak, replacing the AOS and/or finding the vacuum leak will stop the hissing noise and will fix your rough idle.

It is possible that your AOS is going bad and is creating excessive vacuum (negative pressure) in the crankcase and the hissing noise is actually air sucking thru the bad spark plug tube seals.

So I would replace all spark plug tube seals firts and go from there

Thanks for that really helpful post. Most of these things were things I was considering, and this really helps me know I'm on the right path. I had not thought about the dip stick tube, I did wonder if maybe air was getting sucked in through the spark plug tube, but hadn't considered that the AOS could play a roll in that. I ordered new tubes last night.