E30 1987 318i Spluttering

[CFS318]

Can anyone help with issues I am having with my e30 318 M10?
1) Set the CO to the correct value only for it to go to a very lean mixture in no time. This has happened twice. The car will miss and splutter until re-set.
2) At times the car starts but splutters and doesn't rev/idle correctly (very rough). I have replaced the ignition module with a good second hand unit (the fuel filter was replaced about 3500 miles ago & the plugs are good). This helped as the car would start and run OK. Lately it has started playing up again - this happens when hot or cold. A friend who is a mechanic has advised that it could be the module again.
Am at my wits end as I don't want to be spending unnecessary money on parts/components not required.
Any ideas as to what the issue could be will be greatly appreciated.
Many Thanks

[pacerpete]

The airflow meters on this model were notoriously troublesome, the Bosch part number ending in 050. Alas they were only used on injected m10 turds ,so trying to find a good used one will be tricky. The flap used to distort and would drag / stick in the body causing all sorts of running dramas.

If you are confident that everything else is good and there are no air leaks ( Have a REALLY good look at the long trunk from the AFM to the manifold for splits /leaks) and the valve clearances and ignition timing are set CORRECTLY (they seldom are) it might be worth popping the cover off the airflow meter and 'adjusting' the mechanism (mark it 1st ! ) and then resetting the CO%

[CFS318]

Timing and valves are set correctly - car used and serviced regularly.
As for popping the cover of,f the mechanic that helps me service it has already done that when the CO couldn't be set.
Will have a look at the trunck for splits/leaks.
Thanks for the advice.