OK Barry, there is a difference, then, in the way it runs with the AMM disconnected. I think the limp home mode is still supposed to be a rich running mixture, the difference being the fuel is adjusted by engine rpm instead of throttle, so acceleration is insufficient for merging on the freeway.

The problem is, the AMM is still not vindicated. The Haynes measurements don't help; they are just an indication that two very reliable parts in the AMM are not totally defective. I'm afraid those tests are little better than useless. Nothing against Haynes, here, they're just passing along what Volvo provided; same stuff in Volvo and Bentley manuals.

The new information from your fuel pressure measurement takes a lot more of the guesswork out-- you could get an idea if your injectors are leaking by the rate the pressure leaks down after shutdown, if your check valve is holding. Meaning, at least, if you have 43 lbs when you shut it off and 43 lbs 20 minutes later, you can be fairly certain the extra fuel isn't arriving from an injector that is not closing.

So if it is not a leaking injector I still wish you could find a known good air mass meter specimin to swap in.
--
Art Benstein near Baltimore