I do not test AMM as it has been proven that the test you performed is at best inconclusive. Based off the wisdom of this board, the first purchase I made when I got an LH2.4 car was a used AMM that I ran in the car for two weeks to verify "known good" status.

When I have a suspected faulty AMM, I swap it in and that is my troubleshooting.

If the problem goes away, I swap the old one back in to see if it repeats the old behavior.

If the problem DOES repeat I toss the old AMM and get another one (to test in the same manner and deem known good).

If the problem does NOT repeat I have to look elsewhere or hope that it was corrosion in the connection cleared up but unplugging and plugging.

This is one of the most important spares you can ever have. The fuel pump really have be jumpered around and get you home (for example) but if this, the ignition power stage or the crank position sensor go bad...you are stuck. The last two kind of need to be new parts if they fail and are not terribly expensive but a rebuilt AMM is crapshoot (and expensive) while a new one is VERY expensive.