Alright, I think it is your AMM. I have two 89s, a 90 and a 91 with that same system-- I got to playing with the 91 once, trying to learn the LH2.4 signals. It arrived from a seller who buys fixed-up auction cars with an 007 amm in it, so I learned quickly an 007 will at least run the car (pretty well actually) though it should have an 016. The 007 and 016 do at least have the same pin/function at the plug - I was shocked to read in a recent post someone got away with running an 002 in an LH2.2 car - those pinouts are entirely different.

So in my pursuit of useless knowledge I experimented with the so called limp home curve of the ECU, that is supposed to substitute a fixed, slightly rich injector cycle, for the missing air mass information. I took it on a short test drive, local streets only, worried I'd have trouble with a couple of those hills that wear out my bicycle brakes. Its performance surprised me enough to put the term "limp home" in the quotes of skepticism. No, it wouldn't do to merge uphill on a busy highway, but it did seem to get out of its own way fairly well.

Have you tried ebay for the AMM? Your price seems a bit high - even a lot high. Don't put too much value on the Bentley test using an ohmmeter. Do, however, measure the output with no air flow (engine off) and check to see it increases when you blow a bit in (wave air at the opening using a Chilton's) and increases even more when in idle. There are some specifics about voltages and pin numbers / wire colors, I think, in the 700/900 FAQs. Or post back if you intend to go this route - we have the stuff at home.