Slight stutter flathead V12
 

arly Djetronic injection model. Very slight stutter when accellerating, more so the harder it acellerates and most pronounced mid range. Also a slight lumpiness at idle. Exhaust at both pipes have a steady beat but not the even smooth push of a healtjy engine.

sounds like a slight lean spot in the ECU map. could be vacuum leak somewhere.

next gotta figure out how to richen map up, on that area of fueling issue.

of course telephone tuning is hit and miss situation.

Also,

The vac operated fuel enrichment switch is not switching.

The throttle switch is grubby, and/or out of adjustment.

The wires IN the throttle switch are failing, very common.

The EFI loom is starting to cross fire, age related now.

The 2 rubber elbows on the bottom of the throttle bodies are failing = vac leak.

There is a potentiometer knob on the outside of the 3CU unit, and will adjust the HOT idle fuel mixture, just like a carby mixture adjuster.

Stutter, like misfire under load? That is usually ignition. Yes, i see you replaced plugs, wires and cap. Still sounds like ignition. Possibly wire not properly connected to plug or distributor, arcing or faulty spark plug. could be a bad injector, but if they have been cleaned and tested, and it only misfires under load, the injectors seem less likely than ignition.

yes could be ignition , on my early distributor, rotor to cap electrode phasing was VERY important.
hard acceleration requires more accuracy of the rotor gap.

you mention mid rpm range, that could be advance curve going thru a position change.

that could effect the rotor gap.

Thanks guys. Turned out to be a massive air leak, courtesy of the workshop doing one of the two job I have ever farmed out instead of doing it myself :-(