TFT

On the 4.2 engine what does it do and what happens if its not working correctly?

Lexdiamondz10304

It will blow your seals (i.e. Valve Cover Gaskets, Cam Seals/Plugs), plus a few other things, not good.

Panelhead

Used a Vaico. Sad thing is six months later the 20.00 Vaico started honking. Continually honking.
Tried cleaning the Vaico with cleaner and it still honked. Cleaned the original and it is working perfectly.
Used a little Berryman Chemtool to cut the sludge in both.

the_duke

Same here. I replaced my original for no reason other than age and the replacement lasted only a few months before becoming noisy. I cleaned my original and reinstalled. No issues after that.

MainelyA8

I replaced mine mostly due to age, and I thought it was the source of a noise I was hearing in that area. Opted to go with OEM after reading some posts about aftermarket ones failing. Boy, those sure are expensive.

MP4.2+6.0

So summing up, you get what you pay for... The usual Audi refrain. It is the world's most expensive PCV valve, in classic over engineered Audi form. But as the replies drive home, the aftermarket substitute was wasted money longer term.

Fortunately W12's didn't have these. They went with pricier oil separators now commonly found with FSI generation set ups. Those don't seem to have issues on the W12's (some on S8's though), but the plastic connector lines associated with these are what cost you on the W12's as they accumulated ten years of oil vapor and heat soaking.

ltooz_a6_a8_q7

It fixed itself after my tune up 10k miles ago... No more noise :-)

Cheers,

Louis

jandreas

The PCV valve contains a metal spring and a plastic diaphragm (that's it!) Eventually oil gunk will cause the diaphragm to stick shut. So unless the diaphragm is torn, all you need to do is separate the two halves, soak everything in odorless mineral spirits and then clean with q-tips.

MP4.2+6.0

Interesting. Then in turn if you are doing that, just simplify to pump some brake cleaner from a spray can into it while holding one end closed. Then hold both closed and shake. Then spray other side. Repeat a few times. Old stand by on cleaning many things like that. And if diaphragm can't take brake cleaner, on way out anyway.

jandreas

You have to be really careful doing that as most brake cleaner solvents are acetone and will dissolve just about any plastic and paint. I wouldn't use that stuff anywhere near a car, including the brakes!