I was there when the diagnostics were done, the dealer also ran individule test on the Lambda probe, coils, throttle position etc and none showed faults.
When the CO2 reading was taken 5 results were displayed together 3 including the Lambda where
green, but 2 the HC & CO2 reading were red.
The symtons I got were lack of power/hesitation a flat spot at 5000rpm plus lots of noise like loose baffles.
I noticed this morning it smells of rotten eggs, which my wife tells me it has been doing for ages.
Hopefully I get the new cat fitted next week, another £300 on top of the £1000 I have just spent.
I am still in love with it though.
156 2.5V6 S3