MOT Emissions readings for M40

[DaniTD]

Hi! Today I passed MOT checks here in my country (Spain) All fine too the standars here, but I detected a little problem.

On the emissions test, the guy checked my car as it was catalysed, although mine is not. Then, I saw the following results:

At idle:
CO reading 0.15%
HC: 400 ppm

At 2000-2500 rpm:
CO reading: 0.19%
HC: 260 ppm

Lambda was about 1.08-1.1 (I know, I doesn't have lambda and in theory a non-cat engine should run a little rich)

I think this values are indicating a too lean condition, as the engine shakes when hot and makes some misfires when coasting or reopening throttle.

What do you think about this?

Thanks!

EDIT: I read that high HC could be from 1. Improper Ignition Timing 2. Defective Ignition Components 3. Lean Fuel Mixture
4. Defective Catalytic Converter 5. Low Cylinder Compression

Timing is correct and in M40 engine can't be modified (unless distribution belt jumps a tooth), it was verified. Ignition components were tested on a Bosch Service Center and they were ok, this spark plugs set less than 10000km. Mine doesn't have catalytic converter. About lean fuel mixture, all hoses were checked and replaced the faulty ones, changed rocker cover rubber gasket, etc. Another AFM was used and no changes. Maybe injectors? AFM springs on all this old parts are hardened, so leaning mixture?

[pacerpete]

Yes, that is too lean. Before you start 'adjusting' the AFM , you need to carefully check for air leaks. Spraying brake cleaner / WD40 around all the intake / breather hoses and intake manifold area may give you some clues. a good running non cat M40 should produce readings of Ca 1% co and 100-200 ppm.

[Billwill]

Did this car ever have a cat that was then removed?

[DaniTD]

Thanks! I did that, I sprayed all the hoses and parts that have gaskets with brake cleaner and I didn't found any leak. The funny thing is, this low CO readings were always low on the last 3 years, but 4 years ago the CO was 0.83 (good) but with an existing intake leak (the throttle plate was loose and a rubber hose that blocks the vacuum line used for the canister on cat engines was cracked).

[DaniTD]

Did this car ever have a cat that was then removed?

No, the car went out the factory without it as it says BMW and the Technical sheet of the car it has provisions for it though.