Hi, my 420R spec Duratec engined car failed the MOT on emissions. CO was high, lambda was low on all tests. I replaced the lambda sensor which made no difference. Looking back at previous MOTs over the last 5 years I've owned the car (total miles only about 2K in that time), all at the same MOT station, the 1st Fast Idle has always been similar but 2nd Fast Idle has been ok. Since build the car has just under 5K miles. The car is running RBTBs and an MBE 992 ECU (Caterham supplied). From internet research, the high CO and low lambda readings suggest it's running rich. So I've checked the coolant temperature sensor for the ECU and that appears fine (66 KOhms cold, just over 2 KOhms with the Stack Dash reading around 90C). I put the old lambda sensor back in, with a cable spliced into the signal wire to allow me to read the lambda signal voltage. Once warmed up at normal idle, it cycles in the 0.2-0.8V range which is apparently normal but above normal idle (tested between 2-3K RPM), the lambda voltage goes to about 0.9V and stays there, which apparently suggests rich running. Once it's back to normal idle, it starts to cycle again in the 0.2-0.8V range after it settles down. The car hasn't been used since about July and was taken straight from winter hibernation to the MOT, but via a long route with some motorway miles as well to make sure it was thoroughly warmed up. It seems to drive ok. Any advice would be appreciated.