Looking back at the "Neutral gear selector switch" error, which I believe would inhibit fueling at startup if the input (with an auto box) showed the gearbox was not in neutral. That error flag would not be the cause of the engine cutting out, as it would be normal that the gearbox is not in neutral (i.e in drive). So I think that there is an initial cause of the loss of power, and maybe that also causes a glitch that upsets the routine that is scanning for errors.
The only common point between the 'neutral' signal and the tune resistor signal is that they both reference to the chassis ground. For the 'neutral' signal there is a resistor from pin 34 to ground, and for tune resistor it is between pins 27 and 5, where pin 27 also goes to ground.
Probably not relevant, but when you don't have the RoverGauge plugged in do you insert the grounding plug into the diagnostic socket. That grounds pin 18 of the ECU.
When the engine cuts out, if left in gear with the engine being turned over as it coasts, does the rev counter still display the engine speed, if yes, then the primary ignition circuit is still working, if no then points to a problem with the primary circuit.
When it cutout, did it start straight away, or did the engine (and components) have time to cool down before restarting. Normally the coil and ignition amplifiers tend to fail with heat.
A problem I had with my Plus 8 that plagued me for some years. It would be happy for days and months, then just run a bit rough and stop. Sometimes it started immediately, sometimes it refused to start, but then started when it had tried my patience. A few years ago I was in Cornwall, and it refused to start. I decided to check the gap between the pick up coil and reluctor in the distributor, I judged that a bit of card was the correct thickness, I wiped the card through the gap, it seemed correct, put everything back and it started and I didn't get another issue. I didn't leave it there and did replace components, but that's a long story of the current state of poor quality components that are sold as OEM quality, and items sold under Lucas part numbers that are different in build to the Lucas item, it is certainly a jungle out there.
