annoying engine management light

hi everybody.my name is Gerry j.i have a 52 plate frontera 2.2dti lwb.the management light started to give me bother.could not get it to go out.lot of messing about later replaced all vac pipes and elbows in engine bay and the three vac solenoids on the bulkhead.it now stays out,,,,until I come to a junction or traffic lights where I am required to stop.sometimes it comes on but if I give it some revs on the throttle it will go out.a lot of the time it behaves itself.any thoughts would be nice.one more thing ....the 4+4 does not engage.have replaced the actuator on the transfer box.you can hear it clicking in when you press the button on the dash,the green light flashes but will not go out.so there you have it.any help would be much appreciated.

You say you replaced the vac pipes in engine bay so assume you didn't do the ones on the axle?

Have you had the codes read?

a diagnostic has been done but it was vague.it pointed to egr valve,but I replaced that and still no joy.i am a bit slow on these things so I do need to be pointed in the right direction as it were.where on the axle can I find the vac pipes as I am not known for getting under cars much these days.also will this light foul up the mot as it due very shortly.does not affect the running of the car and there is no limp mode at high speed.e.g 75mph plus.

Hope this works. But here's what I have for vac system .take inlet manifold as main vacuum line from the vac pump.

Screenshot_2017-10-07-14-41-32.png

thank you people for your input.if and when it stops raining here I will have a rummage.see what I can find.