Hello Folks,

just put my car in for an MOT, luckily a month early so i've got time to fix it.

Failed on Emissions readings are as follows:

Fast idle test: FAILED
Engine speed: 3150-3650 manual check PASS
CO: <=0.300% 0.765% FAIL
HC: <= 200 ppm 155 ppm PASS
lambda: 0.970 -1.030 1.017 PASS

2nd fast idle test: FAILED
Engine Speed: 3150 - 3650rpm manual check PASS
CO: <=0.300% 0.636% FAIL
HC: <= 200ppm 96 ppm PASS
lambda: 0.970 - 1.030 0.988 PASS

Natural idle test: PASSED
Engine speed: 650 - 850 manual check PASS
CO: <= 0.500% 0.129% PASS

Overall Test result: FAILED

Things i did just before the MOT;
replace spark plugs, new air filter, oil and filter change. The old spark plugs had been in for quite some timeand although the gap was excessive they had a nice colour to them with light grey/brown deposits (no oil, or black soot).
I had to replace the middle and tail section of the exhaust last month so i went under the car to ensure there were no gas leaks.
When I took the car for the MOT i went for a good 40 minute low gear (hot) drive and parked up at the test station with the engine still running to keep the CAT warm.

I had to replace the manifold/CAT about 18 months to 2 years ago. I bought an aftermarket unit, the CAT part did look to be noticably smaller than the OEM item...?

Last year the guy told me that he struggled to squeeze it through the emissions ( I could hear him revved the nuts off the car. ) and i can remember that this was when the CAT was very new... ( reading was 0.279% 10.000 miles ago).

I am still erring towards trying another CAT from a different supplier, hopefully a better one, but any other suggestions ... ?

Mine failed when the cat was blocked, he revved the ******** of it to clear it apparantly