I cannot search, just blank screen So I'll ask nicely

[Spartan]

Hello everyone, I have resurfaced from an arduous task that I seemed to make bigger than the Star Trek series.
As you may know I have been having these strange issues with my E53 diesel, as if it is misfiring. I eventually traced it to an air leak and boy did I get carried away. Still, every vacuum line is renewed, the intake manifold was removed and all seals replaced, the manifold and EGR were decarbonized 100% and the vacuum line to the EGR has a join in it with a small garden fitting that seals the line, thus rendering it inoperable.
Results, well I only got to drive it partially as I then took my wife's Merc W203-C180 and attacked the cam chain. After that I replaced the drivers door as well. So she was driving the BMW for two weeks and getting insane figures for fuel consumption considering her driving style. She was averaging 8.1L per 100k and not a problem with the car. I then drove it for another two weeks before I had a spell in hospital and I managed to improve this by bringing it down to an average of 7.5Lper100k.
Now I am out and back on both feet again, we went for a drive Sat 21st, probably two months since the rebuild of sorts.

We drove 127km one way and it was so pleasant, quiet and power to overtake when I wanted. Day temp was 23c and just fresh air through, no AC needed.
Our destination was reached and the task completed, we turned and headed for home...all was smooth and I had no reason to expect any issues, YET, it happened again. The difference this time was much softer and I actually had time to catch glimpses of the timing of the faults and what the car was doing that caused the problem.


Warning lights are - 4WD and ABS in yellow together.
Occurrence, seems to be either when cornering to the right with combination of braking or harder than a very gentle turn.


The fix to get home - I used the dash code access to reset to default values everything. (The one where you enter the sum total of your VIN digits) This seemed to set the car into a clean mode to drive off once more.


The alternate fix - I just turned off, removed the key waited one minute and then restarted again, the warning lights were out, but the car drove off with some surging effect from the very start and will only travel about 12 km before this warning light combination is triggered again.



Car reaction when warning lights are on - The car will travel a bit further but then gradually it will start to surge more and more harshly. This is almost to the point of engine stalling in one situation, that being a start from a standstill at a stop sign.


In fairness, I have never looked at the ABS rings for cleanliness, I know the disc rotors and pads will be due for replacement soon and I have already replaced the transfer case gear when I had the trifecta light situation.

I have replaced the fuel filter less than 12 months ago and the fact that this is something that happens after "X" amount of time of use does not ring true for that purpose. All the correct sounds for fuel pump are there, even after getting home, I checked and you can hear the pump by placing a tube to your ear and onto the tank.
The car starts and idles first time and every time, so apart from me getting ISTA on my other laptop, which is very shortly. I am asking this question here and now because I have tried searching several times, but all I get are blank pages.


I could be wrong, but I thought I had read that someone had pulled a fuse and made their X5 into a two wheel drive. is this possible and can it be used to test for any faults in transfer case?


All help greatfully appreciated and saving an E53 from the wrecking mode.