If anyone knows the answer I'd be very grateful to hear it.

My Omega starts and idles at 850rpm. Idle is rough until it warms up, with white smoke. It's a 2003 (96K miles), 2.2 DTi Eco-Tech (Y22DTH)
If I raise the rev's, the EML comes on and it switches into limp mode.

My "My Code Reader" shows one error code:
P1220 - (A) Critical System Malfunction 1 (refer to checking procedure: trouble code description) - present.

I've done the following:
Changed the fuel filter, filled the new one with 'Diesel Magic' and run the engine for 15 min's afterwards.
Cracked off the injector pipes and all are getting good pressure.
Checked the fuel system for leaks.
Cleaned the EGR valve and checked it with a vacuum pump.
Checked the vacuum system, found a hole in one plastic pipe, replaced the damaged section and it now sucks 24"/Hg at the solenoids. (Prior to this it was around 21-22"/Hg.)
Seen the (Garrett) turbo wastegate actuator opening as engine revs are raised and checked it with a vacuum pump.
Disconnected the air filter box, allowing open air to the MAF sensor.
Swapped the MAF sensor with a known good one (both are Bosch OEM).
Checked the intercooler hoses. They're sound but there is a coating of engine oil in them, so it may be in the intercooler too. (No excessive engine oil loss though.)
Disconnected the MAP sensor which made the engine run lumpier. The MAP sensor was replaced around 1500 miles ago with a Bosch OEM part, so I believe it to be good.
Replaced the crankshaft speed sensor with a new Bosch OEM part.
Fuel is Shell V-Power (roughly half a tank)

This is the relevant measuring block info at idle, before the EML comes on:

Desired Injection Start = 4.8 CA
Actual Injection Start = 1.1 CA

Desired Injection Quantity = 7.4 mg/strk
Injection Quantity = 5.7mg/strk

Pump Speed = 411 RPM
Engine Speed = 824RPM

Mass Air Flow Sensor = 512mg/strk

I don't have any higher reachable engine speed other than idle, because if I lift the rev's (even gradually) the system goes into limp mode.

Thanks for your time.
Regards
Steve