Can't work this one out - my 2.0 16V XSi, for the last 2 years now, has struggled to pass on emissions. The numbers really don't look right:

from 2009 MoT test:
Fast idle test 1 (fail): CO 1.099 (limit 0.300), lambda 0.975
Fast idle test 2 (pass): CO 0.006 (limit 0.300), lambda 1.008
Natural idle test (pass): CO 0.434 (limit 0.500)

from 2010 MoT test:
Fast idle test 1 (fail): CO 0.442 (limit 0.300), lambda 1.010
Fast idle test 2 (pass): CO 0.054 (limit 0.300), lambda 1.006
Natural idle test (pass): CO 0.116 (limit 0.500)

What seems odd is the huge difference between FI test 1 and 2 (in both cases), although I am pleased that both idle tests this year show a much lower value to start with.

I assume the perfect lambda value is 1.000?

After last year's MoT test (where they advised that emissions struggled to pass), I changed both lambda and cat, so was a bit disappointed that it still appeared to struggle this year (although they didn't advise it this year).

Any thoughts on this welcome - they did check the oil temp for the second FI test, and recorded it as 83. Not sure where else to look for ways to improve the chances of it going through first time.

(I did think at first that my fitting a 6 exhaust manifold had messed things up, but I had the original on last year and that was the same.)