My A6 actually stopped the machine on the emissions test on the MOT, and the Lambda sensor thing, air flow meter and coolent sensor where all coming up with problems.

I took my car to Riverside Motors in Darwen Lancashire who are a VW & Audi specialist and they sorted it !!!

It was the Probe !! dunno what it is... but it was 40 + vat and fitting and all sorted. All who having a problem around that area get the probe looked at.