Help! My car has just failed emissions test as part of its annual check (in UK) so its off the road while I get it fixed. Engine is a LS376/480 fitted to a BMW Z3. Its running in (pure) closed loop fine with small fuel trims. The tester was getting Lambda 0.95 to 0.99 - never over 1, at any speed. It needs to be in range 0.97-1.03 to pass. Its also possibly causing high CO - target is 0.5/0.3% idle/fast idle and these are not met. Values come right down when the engine is revved, when I assume the CATS get hot enough to work, but it soon goes over range as they cool off at idle. The exhaust outlet looks rich and its smelling rich too.
So the question is how can I adjust the settings to change the target stioch mixture? I cant see anything other than voltage limits for the o2 sensors.
I have check the manifolds and there are no signs of leaks anywhere.
I a begginer with tuning - I managed to get the basics sorted (MAF calibration etc) but my knowledge has run out! Existing tune is attached. Help would be most appreciated - I have a big car show planned next weekend which I will miss unles I can sort this quickly.