My 156 v6 failed the Swedish equivalent of MOT a couple of weeks back. This is driving me nuts...
CO 0.7 (0.5 max) - fail
CO2500 0.9 (0.3 max) - fail (fast idle)
HC 212 (100 max) - fail
lambda 1.03 (0.97 to 1.03) - pass
I have replaced this far:
1) The thermostat (was stuck)
2) cat (I had one laying around)
3) lambda sensor
Non of this changes a thing. I made my 3'd attempt today and the values are STILL exactly the same.
If I look at the lambda sensor in dnecudiag it jumps between 450-1100 mV at idle. If I hit the throttle it drops down (briefly) to about 280mV.
To me this look like the lambda sensor is telling the ECU that it's running rich, but the ?!#&& ECU just isn't listening...
Any and all ideas are welcome at this point...