It fails at 2500rpm only with CO 0.5~0.6 and Lambda 1.04~1.05. How can it possible be that emission fails because of HIGH CO, and HIGH lambda reading... It means that engine runs rich and lean at the same time...
High co and high lambda could be because of exhaust leak, but I checked it, by blocking exhaust and no hissing or anything.
(Air filter changed, maf changed (previous was defected, bought new one (got maf'ed...) bought BOSCH OEM, works perfectly).
I tested O2 and AFR sensor with obd2 scanner, when car is at operating temp at idle, o2 sensors works nicely. Afr sensor I think works too, when holding 2000rpm, and instantly press to 4500rpm and let go, afr sensor reacts to that nicely. So sensors not a problem. (maybe they're laggy thats why..)
Another thing what I think might be a solution, but i'm not sure. Maybe it's spark plugs or ignition coil problem ? Maybe a one or a few cylinders misfires, while others works perfectly, and that causes Rich and Lean condition at same time. Before testing I gave car a good 40 min highway run at 4.5k - 5k RPM. So catalytic should be okey, or it's totally defected..
What do you guys think, I will appreciate all answers! (Car BMW,engine n42b18)
EDIT: I want to add a one more thing. When I increase rpm above 2500. CO and Lambda reading also increases. So when increasing engine RPM, CO increases and lambda increases. I think that means, that by increasing RPM, it gets richer and richer, but at the same time more air comes out of exhaust... -Looks like an exhaust leak I will investigate more about this. Or could be bad ignition coil or spark plug, because by increasing RPM not all fuel burns out and is thrown away into exhaust, but that would increase Hydrocarbon HC, but it is FINE... Maybe fuel is partially burned and not all of them, that's why CO increases, and if there is AIR in cylinder that is not used to ignite all of the fuel, it could show HIGH CO and HIGH LAMBDA at the same time ? Or i'm thinking wrong there.