Too low emissions 0.15% CO

[DaniTD]

So, previous year I took the car to a garage to adjust the CO and the guy touched the AFM toothed gear to adjust it. MOT passed, Car on winter was very sluggish because of the moron that touched the AFM. So I got a new one untouched.
The previous year I passed MOT with 0.27% CO (the AFM "adjusted" by this guy)
This year with my new AFM 0.15% CO this is not good, I read it should sit between 0.7-1.4 on non-cat M40 engines.
No air leaks found, what can be wrong?

Cheers

[sweep]

the afm needs adjusting to richen it up

[DaniTD]

Knob is at full clockwise AFAIK, the trunk floor gets hot on the exhaust side

[sweep]

if it wont richen up sounds like you have a air leak..possibly on the inlet manifold.

[Brianmoooore]

the afm needs adjusting to richen it up

If it's an untouched AFM, it does NOT need adjusting. It was set correctly at the factory, and if adjusting it makes an improvement, then you are simply masking one fault with another fault, and making diagnosis near impossible - one of the reasons there are so many E30s around running way below their true potential.
Very low CO indicates an engine that is running very lean for whatever reason.

[sweep]

air leak yes.

[DaniTD]

I checked for air leaks and for god's sake.. I didn't found anyone. I tried with carb cleaner on all rubber hoses, joints and gaskets with no luck.
When the car is hot and I drive at 1800rpm and then I release the gas pedal, you can hear sounds on the exhaust like backfires. Sometimes when I'm coasting this style, if I apply gas again you can hear another backfire on the exhaust and the car makes a little push forward.

[driftwood]

Do you have a standard air filter? A high flow performance air filter may affect fuel mixture. A backfire could also be due to a leak in the exhaust. It could also cause a lean idle c.o.% if it's big enough. A lean idle mixture isn't a problem if your engine runs ok. It doesn't necessarily mean the fuel mixture will be weak at higher revs and with a load on the engine. Only a session on a rolling road could tell you that. To give you a rough idea, you could take the car for a thrash and then take a look at the spark plugs. Did you have high h.c. readings? If so it could indicate a problem. Do you have access to an exhaust gas analyser? I am not an expert btw. Maybe a service might help.