Would be very grateful for an help or info into a problem that has persisted for the last year or more and cannot be solved.

Mazda 6 diesel, common rail, no dpf.
Car will start up, no lights and runs for about 30 seconds at idle, then it will suddenly throw itself into limp mode, running very roughly with the EML illuminated. Light can be put off with scanner, but will do the same thing again almost imediately.

However once the car is driven down the road a bit, constantly reseting the EML, it may then drive for up to 40 miles with no problems or check lights, as long as the car is driven and not sitting at traffic.etc.

Once again after sitting at idle for a short time, the car wil snap into limp mode and won't rev up over 2000rpm. Code is P0627-Fuel pump control circuit A Malfunction.

I know of common problems with pumps and SCVs and injectors. All have been replaced with no change. Even put old parts on another mazda 6 and it ran fine.

Does anybody know of anything that could be causing this to happen? Any suggestions would be gratefully accepted because I'm at my wits end looking at it!