Hi
Connector 2 on MPEM was the one with a little corrosion. Pulled the complete MPEM out this afternoon and cleaned all connectors, reinstalled - no change.
Checked main air hose/line from compressor to rail - no muck or moisture etc.
Pulled fuel filter and checked clean/flows well - no problem.
Wadya reackon invest in a couple of fuel injectors? in for a penny in for a pound...
I am now at the point where pottering around with the beast has become my hobby

and even if we buy another unit, because this one is not much use at the moment, I will keep it and continue pottering unitil it works!!!
Alternatively maybe I need to make a visit to a friendly dealer for hookup to the magical machine to narrow down the fault.
eDiT: Being doing some reading, forums and the service manual, lazy Saturday afternoon pondering GTX Di and the meaning of life (42)..... Given the test results I have been getting (
putting aside voltage issue for a moment and focusing on idle) it looks to me, and my knowledge of Di's
wouldn't fill a thimble, like either air pressure as previously suggested or TPS.
I will build a rig so I can test air pressure, got a gauge just gotta work out what parts I need from the local auto parts mob.
Am I correct in that TPS can only be checked and adjusted with CanDoo / BUDS etc?