Reset the AFM

[Connieblau]

Morning all, hoping for some assistance!
Backgroud:
After 100,000 miles servicing, we have parted with the local (friends) garage, on mutual grounds and under a bit of a dark cloud. Early last year ago my wife's '89 320i convertible was booked in for an MOT and she was told it was time also for a cam belt and a coolant pump.
It turns out the business owner was retiring, and the friendly banter of the day was he was starting to forget things. There were two items initially to notice. The bonnet hinges had not been tightened and it ended its travel first time opening mostly up, but at a 45° angle from vertical. Second thing there was no new water pump, this put the cam belt in question, there was nothing entered in the service book and the paid-for invoice at this point was not forthcoming.
Moving on......arriving home one day a few weeks later the car engine had a light knocking sound.
This could now be any manner of things. 50 years ago I was capable of dismantling a Triumph Stag and a VW Beetle, but nowadays who knows? I started on the assumption the wife had filled up with some lower octane fuel, but pumping it all out and replacing it with the best was no answer. The months following I've cleaned and checked everything including another cam belt, new water pump, sonic clean injectors, tappets, tappets, tappets, plugs oil twice.
The last thing (I hope) is the AFM. Over 200,000 miles the AFM has not been touched, until that last visit to the MOT. The black plastic 'cap' was GLUED -on so it took two days to release, (now a little damaged) and there is no longer a red cover to the un-measured air supply for idling. The number 15.9 was still hidden/smothered in the yellow anti-rust chromate coating.
I am now stuck having no way to know what abuse might have violated the 'never open' secrets of the air/petrol/granary mix that goes for fuel. I have read loads of internet stuff trying to find out the following please help if you can with:

I have a video I seem unable to upload, so have put in an image (can send a video separately if anyone 5inks they can help) of the corrugated potentiometer:
A. What do the white numbes signify?
Is a '1' number a 1.6 litre car, and '500' number a 3.0litre car with other engine sizes between and beyond into 5 series? Are they the mileage ? Impossible without taking off the cap.

B. The video shows a still-knocking COLD engine at idle which (take my word) is 760rpm. The potentiometer slider is around 40° rev range the secret bypass air is adding itself, and the idle valve is also adding its' ha'pennyworth. Seems a heck of a lot of air for 'idle'.

C. Turning back time to October 1989 with a completed car ready to drive out into the car park how did the tech -team know which number to start on before they fine tuned the sprockets and checked the exhaust emissions before they punched in the tiny 15.9 numbers.

D Does anyone in the UK know how to do this? BMW Swindon offer to service E30's of any age, but when asked direct they don't do this part of a service any more.

Thank you in advance for any and all advice!
Trevor, Wiltshire.

[Speedtouch]

I would suggest checking some basics such as tappet/rocker clearances and leaks around the inlet manifold and vacuum hoses before attempting to adjust the AFM. Also, remove the spark plugs and check they are gapped properly and showing the correct mixture colour (biscuit/light tan).

However, if you feel you need to, there are various You Tube videos on how to go about adjusting the AFM, such as here:

[Connieblau]

Thanks. So no-one knows ? No enthusiasts left maybe, TV programme Bangers & Cash auction them quite often but the rare E30 that is televised always has a detrimental comment about complicated engine management. Never seen an M3.

[Speedtouch]

This thread may give some pointers:
viewtopic.php?f=2&t=278810