The crankcase ventilation system on the AAN is operated mechanically and is not controlled by the ECU. The only connection (so to speak) is the ECU controls boost (and vacuum) depending on the throtttle position and the crankcase ventilation system function changes with boost/vacuum it sees.

Under boost, the oil vapour-laden crankcase air goes to the MAF to turbo hose; under vacuum it goes to the intake manifold. This is what VAG says about it (Note: Diagram was corrected to agree with the text):




Suffice it to say, if there is a rip in one of those hoses or the PCV (non-return) check valves is stuck open, you can have problems.

Personnally, I replaced both valves when I did my first FMIC.

The Pressure Control Valve in the above diagram is called a "pressure regulating valve" in ETKA and has a 034 129 101A part no. (Note: 101A has been superceded to 101B and apparently its less expensive) (Ref: Item 3, Kate's photo album 103-89 as below). The non-return valve is a check valve, aka positive crankcase ventilation valve (PCV) or in ETKA, "bleeder valve". Its a one-way ball-type check valve so it needs to be installed in the correct orientation. PN is 035 103 245A. (Ref: Item 10, Kate's photo album 103-89, as shown below):



The breather tube in the above connects to Item 23 (breather assembly) which is a flange assembly pressed into the block, as shown here:



Here is Illustration 133-70 from the N80 Evaporative Emissions post where Item 14 in the first diagram becomes Item 1:



Here is the bleeder valve (PCV) valve, as shown in the Arizona Autohauz on-line catalogue:

Here is the pressure control(regulating) valve from the ECS tuning website:



Note the orientation of Item 10 the PCV valve ("nipple" up). This shows better here:





There is also something called a "flame deflector plate" ((Ref: Item 5, Kate's photo album 103-89) (PN 035 103 477A) located just downstream (towards the engine) from the pressure regulating valve. This thing is supposed to stop flames travelling in these hoses - might just be a means of condensing oil vapours - no idea. Here is a photo:



It's supposed to look like the clean one on the left, not like the one on the right.

HTH