Firstfives.org

CPALMER
What year is your car ? .....older style aux air valve ?

Back from merriment...!

That is a good site I found some time ago that explains how an AFM works even if it is addressing the Porsche crowd.

To address cpalmer's thoughts:

The 'click' arrangement is a coarse setting that sets how much resistance to moving air the flap in the AFM is subjected to. The adjustment screw under the AFM is a fine tuning of that setting and the one we adjust for proper idle mixture. You can mark where it is now, lift the springset and move it a click or two in either direction, but that is the same as hooking up the AFM to the throttle body without the air filter and lightly pushing on the flap. Pushing enrichens the mixture at idle, and like myopes (near-sighted folks who always want more 'power' to see in the distance, to a fault) the M30 engine is always wanting to run richer , so pushing on the flap will improve the idle - to a point - until it is too rich to run smoothly, but most importantly, way beyond the stoichiometric air-fuel mixture of 14.7:1 for complete combustion.
These terms regarding 'clicks' get bounced around without the understanding of the engineering designs. The above is just for explanation, you really don't need to do that, and it won't affect your worn wiper track. (see my post on AFM adjustment as printed with permission from the kind folks at Metric Mechanic in the archives for more info.)
What will affect it is to either 1) bend the arm, or 2) remove the entire carbon board (several things must come off first, and you MUST mark where the wiper arm lives at rest, so it can go back in the exact same location - that affects the entire range of signal sent to the ECU) and elongate the mounting holes slightly so that the board sits in a different position from original. I believe it can only move downward. It doesn't take much. Either of these methods will cause the arm to track in a different arc. Notice there are two points of contact on the wiper arm, that was a redundant factor built into the design. (But it wasn't meant to last 30 years). So we improvise. This will address your worn wiper arm condition only. If there are other factors needing addressing, they must be attended to one at a time.

I would add a couple of things to the AFM writeup.

1. Always mark it. It's spring loaded, nothing you can't hold back, but it will be more than you expect and jump when you release it. It will, believe me. Do that and you're lost.

2. Unlike on E28s, small adjustments seem to make a big change. I tried two notches richer one time to try and clear up some warm up issues. Sometimes it would get into a ultra rich cycle, where it was reading O2 off the sensor due to misfiring due to the ultra rich condition. At that point it wouldn't restart and run until I disconnected the O2. It only did it 3 or 4 times, but once in an intersection at what was once a red light got me to change it back to stock in a hurry. Not a good feeling with traffic backed up and running out to open the hood and pull a wire off.