Do you have rich mixture problem? Do you smell gas from exhaust?
I had similar problem three months ago for my 740GL, 1990. Mine has Regina system and have air temperature sensor and air pressure sensor not AMM.
In my case idle was not stable and very poor acceleration. Diagnostic unit said nothing is wrong. So, I did everything like you did for cleaning and put new distributor cap, rotor, spark plugs and wires. No change. I replaced fuel pressure regulator. No change.
Finally, I found small crack at the connecting site of air pressure sensor hose on throttle body. This sensor is located above drivers side suspension turret and has thin yellow hose (may be three feet long) connected to TB. At connecting site, black soft rubber hose is used. I found crack on this black hose and replaced it with smallest ID vacuum hose available at my parts shop. My problem gone!
The air pressure sensor misjudges the pressure of vacuum manifold and send wrong signal to ECU. Because of this FI system put more gas than it needed. This makes rich mix and poor acceleration.