When I first saw this there were a load of codes relation to the front oxygen sensor. I replaced this and the fault codes have not returned. Customer also reports that car drives much better. However the emissions did not pass the MOT.

I replaced the Cats (there are two) with after market type approved units and although the emissions are a little better they are still not better enough

Idle

HC 249
CO 0.229
CO2 15.56
NOX 0
O2 0.08
Lambda 0.988

Fast Idle

HC 56
CO 0.410
CO2 15.51
NOX 0
O2 0.03
Lambda 0.986

What is wrong?

I cant help feeling that the rather high HC at idle is a give away. When I go back to it I am going to check the camshaft timing. (I can see that somebody has replaced the timing belts at some point) But at the moment I am just frustrated with it.

Even more frustratingly there does not seem to be any mechanism via VAG-COM to monitor the primary O2 sensor behaviour!

Any other suggestions for when I go back?

TIA,

Paul