This is an absolutely standard design fault on this chassis which VAG have done nothing about. It also affects VW and Skoda clones.

Typically, rather than recalling the vehicles and correcting the fault, VAG have covered their tracks by putting "inspect plenum chamber drains" in the service schedule. So, if this has not been done, you have no redress.

There is in fact a VW branded TSB detailing the fix for this problem, which is to remove the self-blocking bungs and replace the useless open-cell foam seal on the pollen filter housing with a bead of mastic strip. I have done this job on my Superb and the original seal is not fit for purpose.

I think you may have to bear the cost of this dreadful piece of design - which also makes the car dangerous due to rusting of the servo housing - but make sure you get the cause rectified properly. No action from VOSA, despite a car of this weight being unstoppable without a servo.

The VW TSB is 443/06 and the mastic strip needed is AKD 497 010 04R 10. Best of luck - put your energy into fixing it rather than arguing with VAG who have been there a thousand times. Then vote with your cheque book.

659.

If you end up with engine fumes in the plenum chamber after bung removal - you have a problem. Some of the petrol engined B5.5 variants have crankcase breather pipes in that area which are prone to leakage. Other makes of cars manage with holes in the plenum base you could put several fingers through - they don't get blocked either.

I think the animal is a Platypus. My platypus had a cruciform bill which is perfectly designed for the job of getting blocked. Given the safety critical necessity of keeping water out of there, I would remove all bungs (there's one under the servo with a pipe running through it) without hesitation. These cars should have been recalled for this as effective brake failure and engine damage can result.

It's also essential to change the foam seal (which will be split and sodden with water) for a strip of 10mm mastic asap.

How do VAG have the affrontery to sell vehicles in this build state for the sake of 10 ps worth of sealing strip?

659.

Iankem, you mention the plenum drains but not the pollen filter housing.

You need to remove this housing & discard the original foam seal, then either get the replacement seal from VW as highlighted by 659, or fill the recess with a mastic or silicon sealant & make sure it is proud of the recess. Clean the area the filter housing sits on carefully as it will be full of crud, before refitting.

The carpet & thick foam underlay really need to be removed from the front passenger area to dry it properly. I did this by removing the passenger seat (don't switch on the ignition while it is removed or you will have the Airbag light come on, which can only be reset by the dealer or VAGCOM) & cutting the carpet accross to the centre console. Dry out the CCU ECU & associated plugs, check inside the CCU for water. Dry out the plugs & check for corrosion, some wires may break off if it has been wet for some time. Also check the near side off the footwell wall where there is a lot of wiring & more connectors.