I would get another mechanic. If he suspecs the AFM he should check it. The specs are listed. Maybe someone else with stock EFI knowledge can help though.
I just read your other post. Your ECU is not OBD I or II.
My .02... I Would put a timing light on it and rev it to see if it stays were it should or moves all over. A dial advance light would be better so you can check as it adds timing. Either way you will see if it's steady, increases with rpms or is all over. If it's knocking at 2K it's just over advanced, not detonation, especially if there really isn't any load, and no boost, I would guess more than 40*.