Thread: Crankcase vent valve

Hi all, after a bit of investivation in to my S3's "cylinder bank 1 running lean" problem, i have checked the seal between the CAI kit and the car, i have changed the plugs and yet i still have the light coming on and a reduction in power.....

Now, i have been reading about this crankcase vent valve and it mentions something about the car running and removing the oil filer cap.

I have just removed the filler cap (it was fairly tight) and the car sounded as if it wanted to stall and sounded rough. I put the cap back on and all seems ok.

Do i have a faulty valve, or is this normal?

This is starting to get to me now as i love this car

Cheers, Louis

No thats normal mate, these cars run PCV so by opening the oil cap you are just creating a big air leak. Have you changed the coils?

Yeah the coils were replaced by audi in september 2011. I will change the plugs tomorow i think.

no thats not normal. the oil cap shouldnt be held down by vacumm.

think about the valve, its got one breather pipe going to it, its also bolted to the rocker cover which is another breather route. now the pipe to the inlet manifold...... under idling its under alot of vacuum...... on boost quite alot of pressure.
this valve has to balance these running conditions so that it can take any crankcase pressure into the inlet manifold but without putting the crankcase under pressure or vacuum created in the inlet itself.

if when you remove the oil cap it feels held down by vacuum in the crankcase and the engine struggles when you remove it thats a sign in itself that the valve isnt working properly.

Revving on Idle

Well, the cause of my cylinder bank 1 lean error was............................................... .................................................. .............................. A DIRTY FUEL FILTER!!! AND I MEAN FULL OF WATER AND MUCK.

only ever filled up from tesco with momentum.... bad times.