Having many problems with TDI going into safety operating mode on early morning startup and also fluctuating engine revs i have established the following:
Blocking off the EGR valve resolved black exhaust smoke on hard acceleration but no change to other issues.
Changing the fuel filter gave me loads of problems with air in the fuel line but cutting off 10mm off the feed line from the filter and refitting cured this problem.No effect on the running or safety mode.
I was using vagcom software to clear the fault codes so i could get out of safety mode. If i started the engine from cold and let it idle it would go safe after 15 seconds. If i kept the revs high or just drove off quickly it would stay out of safe mode.
Now strangely when i was trying to start with air in the fuel line i needed to hold the starter for up to 30 seconds and keep cranking until it started to fire up. (it took three days of this) but this time the fault cleared itself as i watched the gear illumination go back to normal on the dash display. How would that happen? It must be a clue to my problem. Only goes safe mode when cold and idling and can be cleared after 30 seconds on the starter.What controls the cold start as after it warms up it will run ok all day.
I have the clue but don't know the answer?? Help please.

 

What was the fault codes?

 

Engine:- 0550 start of injection regulation 17-10 control difference intermittent
Auo box:- 18625 load signal error from ecu P1857 - 35 -10 intermittent.

Went out this morning to test my theory - chilly morning. Started on the button but i kept the revs to 1500 + for the first minute or so and no safety mode popped up it was fine. it then idled ok.
so it is from a cold start and idling that gives the fault. there must be a pressure problem in the hydraulics maybe but once the oil gets round after start up it all is ok. It could be a sensor or a pump but i have no way of knowing. Just my guess.