Today I was going to pass MOT and use it as the start for my turbo project. Instead the car failed testing. Overall they said the car was in perfect condition, but they fail it because of the emissions tests. I now have 30 days to pass a retest or I am not allowed to drive the car. Needless to say, I won't be buying parts for my new project until the car is road worthy again. You guys have similar tests and thresholds, referring to "EU 82.1.2" standards. CO value at idle speed: 0,4 (0,3 is highest permitted value) CO value at fast idle speed (2.500 RPM): 0,5 (0,2 is highest permitted value) NOTE: other exhaust emissions values were within range: Lambda 1.0 (0.97 - 1,03), HC 68 (200). My thinking is that 02 sensor(s) is OK because other values are good, and car runs really well. I am running a 034 Motorsports high flow cat, could that be the issue? Has anybody passed MOT with this cat before? On the other hand, my old WRX STI passed with a 100 cell cat without a problem. The cat was warm prior to test - I had driven aggressively for almost an hour just before the test so it was absolutely at good working temperature. More info: - Oil change and engine flush, late 2017 - New spark plugs (June 2018) - Runs on Shell V-Power - HFC at working temperature during test Any and all help welcomed! EDIT: My lambda is 1.0 which is a perfect 14.7:1 air to fuel ratio. That should mean that my mixture is OK (good actually), right!? Meaning its an issue with the HFC not reducing the CO's.