Here's an interesting story regarding a recent experience with the air mass
meter in my 1992 900S: For about the last year, I experienced intermittent
Check Engine Lights (maybe once a month or two, at first). The frequency
gradually increased, until I was seeing the C.E.L. pretty much every day. At
the same time, the car's idle became rougher and rougher, and it nearly stalled
a few times. All of the stored error codes had something to do with the mixture
being too lean (e.g. bad mixture, lean mixture, oxygen sensor, etc).

I suspected it might be the AMM. I read a post in this group that suggested
that unplugging the AMM could be diagnostic (i.e. if unplugging it improves
performace, the AMM must be the problem). And so I unplugged the AMM, and
quickly discovered that the car won't start with the AMM unplugged.
Disappointed, I plugged it back in and drove off.

To my amazement, the Check Engine Light and drivability problems were totally
cured, and have remained so. I don't know why it worked, maybe the plug was
gradually coming loose from the AMM? Anyway, this was the cheapest, fastest,
and easiest car repair job I have ever done.

John