If the EGR then only operates below a certain temperature, how can we control the N75 to expel extra gas when EGR turns off?

Also, one of N75 maps has a sudden drop at approx. 6IQ to 25% then rises back up at 25-30IQ with 50%. I presume this may be for the regen as the EGR isn't used at that point.
So can I use this timing as a guide for changing n75 with egr off, but not as severe as the 25%.
When in regen, I presume SOI, RP, etc are increased to get temps up and this serves the extra gas like if the egr is shut.

I preffer to keep open vanes settings and lowered boost for both conditions, EGR on until certain temperature and EGR OFF. I dont feel so much difference.

Tonight, I will mostly be putting my EGR and N75 back to stock.
It's approx. 200 over on the boost whatever the N75 when logging, so I want to test it stock.
Something somewhere isn't right, so I need to check stock readings first to compare.
The realtime mpg readout is guzzling the fuel and used to be quite controllable, but it can fluctuate over 30 mpg and back again driving on a flat road at constant speed. Is this the PID trying to compensate? Damn cars!

Just wanted to comment on something i'd seen on second and third posts of the thread, ie. the purpose of EGR.

Diesel engine-out NOx emissions are actually LOWER than spark ignition engines. The three way catalytic converter fitted to SI engines since 1992 is astonishingly effective at reducing NOx, but cannot do so with lean (ie. diesel) air-fuel ratios.

Basically, the narrowband lambda probe in a the SI engine operates in closed-loop feedback with the fuel injection system to ensure a perfectly stoichiometric fuel-air ratio. Oxygen atoms combine with Nitrogen atoms at high temperature. This occurs naturally in lightning , bringing otherwise unreactive Nitrogen into the food cycle, without which plans would be unable to synthesise proteins.

The problem is these man-made emissions are too much of a good thing.

Now, in our perfectly stoich petrol : air mixture, for every oxygen molecule that chose to combine with nitrogen instead of petrol, there is going to be a petrol molecule that couldn't find enough free oxygen to burn completely, because there is no spare oxygen to go round. These partially burned petrol molecules form carbon monoxide and unburned hydrocarbons.

The three way cat peels the oxygen molecules off the NOx, to make pure Nitrogen, and hands those oxygens over to Carbon monoxide molecules and unburned HC, so they can complete their oxidation to CO2 and H20. This process only works because CO2 and H20 have a greater affinity for oxygen than nitrogen, and because there is zero free oxygen in the exhaust, so no other source of it for them.

How does EGR reduce NOX?

The chemical reaction that combines N and O to form NOX is actually a two-way reaction. NOX splits back into pure N and O under the temperatures and pressures of combustion too, so eventually an equilibrium would be reached whereby it is breaking down as fast as it is being formed and the concentration stops increasing.

So, the first effect of EGR is to reduce the concentration of N and O in the cylinder, which slows down NOX formation.

The second is to increase the concentration of NOX in cylinder gases, by incorporating NOX from previous combustion cycles. This increases the rate of the reverse reaction, which splits NOX.

The final effect is to increase the thermal inertia of the cylinder charge, so it doesn't heat up to as high a temperature when a given quanitity of fuel is burned. You are replacing O2 molecules with H20 and CO2 molecules, which take up the same volume as the O2 they displace, but have additional mass on account of the extra Carbons and Hydrogens and thus have more thermal inertia too.

The downside of course is that by reducing the amount of surplus oxygen in the fuel charge, you're increasing soot production.

Lean NOX catalysts are starting to see use in diesel engines, but they require the addition of another substance (Adblue) to persuade the O to part company with the NOX molecule. There are numerous catalysts that can facilitate the reaction, but each works best over a rather narrow temperature range, so a mixture has to be used to provide full coverage over the range of exhaust gas temperatures Diesel engines are subject to according to load.

Nice Theory.
Final conclustion regarding benefits of EGR(excluding NOX) ? Can EGR help for something? economy/energy/efficiency or another things? For diesel cars i mean.
I see that with EGR on, the engine runs smoother, less noise, better starting in 1st gear. I didnt test yet fuel economy with and without EGR.