HDI rail pressure fault codes

A 2002 Peugeot 307 2.0 HDi was presented with multiple fault codes.

It was in reduced performance mode, and driving the owner and a few local garages crazy.
The codes would clear and return, and the car would drive far better with the air mass meter disconnected.
This has led to incorrect diagnosis of the AMM, and the replacement of many components with 2nd hand parts to try and eliminate the cause all without success.

A quick scan produced the same result as the previous garages, DTC's.

The codes were as follows;

P0190 rail pressure sensor


As the Rail Pressure Sensor is a primary input and sure to place the ECU into reduced performance mode it seemed logical to start here.

A quick KOEO test showed a good 5v supply, a signal of 9.19V and an earth of 4.98V.

Bingo the first problem to solve, I unplugged the sensor hoping the readings would change however they did not. Next I tested the wiring back to the ECU pins, all OK no shorts or open circuits. The problem must be in the ECU! To prove the fault I provided the rail pressure sensor with a temporary earth direct to the battery, the codes cleared.

The ECU registered normal rail pressure during cranking and the engine fired into life.

Then suddenly the engine cut out.

A quick code check now produced;

P0380 Glow Plug/Heater Circuit "A" Malfunction.
P1112 Diesel high pressure monitoring system Malfunction. P1465 A/C Relay circuit malfunction

It was the rail pressure code that caused the engine to cut out.
I cleared the codes and started the engine again, the rail pressure rose as expected during cranking, then settled to around 360 bar then climbed to 400 bar and the engine stalled. The duty cycle of the pressure regulator was fixed at this time and the idle speed constant. So what caused the rail pressure to rise?