>>> would i be right in saying the ECU appears to be trying to control the fuel pressure via the DRV as it is seeing an issue with the ZME? <<<

That's what it should do, but if the fault is still present we have to look further.

So we are saying that at idle with the ZME disconnected the engine speed is surging and the rail pressure is following suit?

That's starting to sound like a DRV issue.

If so what is the supply pressure doing at the same time?

Mark