Brake Booster Check Valve Issues
Something for you guys to watch out for - when this goes - all you hear is a low volume high pitched sound. Almost inaudible - can only hear it in the cabin with the radio off & windows up.
Problem is this is a vacum leak and will push your fuel trims all out of wack.
Happened to me a few days ago. I just barely noticed it & the tech even had a hard time hearing it. Found the cause using a stethascope (sp). Brakes were okay. The new TSB's put together by JMVorbek lists it as white noise.
It leans the crap out of the trims - I put my Preditor unit on to look at the car and the LTF's went from normal -3.91 to +7.81 @ 65mph. Not good.
Car is going back in Wednesday to get a new unit put in.
2004 Black, A4, (aka the Black Demon)
390ci AES low compression
PB 1.611, 11.732 @ 115.22, DA +1,973 @ 4,005 lbs
1.566, 11.585 @ 116.22, DA +960 @ 4,010 lbs (Nasty Headwind)
1.538, 11.352 @ 119.16, DA -2,340 @ 3,960 lbs