This time – a different story. The customer’s fight with the N43 series engine has reached a dead end.
The car has (as if) new injectors installed; VANOS solenoids have been replaced; the NOx system has been repaired.
As if there are no fundamental problems – the engine uses Stratified charge, as if all adaptation data in INPA are correct. But at the same time, the owner of the car has observed two problems:
a. during cold start, a moment after the engine is started, idle RPM shivers (and it is not a well-known bug because it also happens a more extended time after the start);
b. increased unevenness of the engine performance observed if/when the DME activates VANOS.
I will start with the second problem. The electromagnetic valves of the VANOS have been replaced, and everything should perform perfectly! The owner of the vehicle sent me the data log. Here is one of the graphs:

Blue: required oil pressure;
Red: oil pressure, reported by the sensor.

Pay attention to the marked areas:

The required and measured oil pressure is significantly different during these moments (and even in a range of moments – in smaller amounts). In addition, not the torque nor the RPM of the engine during these spikes (drops/increases) does not differ significantly! So – the problem is caused by the oil pressure regulation system itself, not by some external conditions.
What has happened to this system? There are 2 options possible:
a. defect of the sensor (suddenly it reports incorrectly high oil pressure);
b. regulatory valve tends to stick in the open position.
This time it looks, that exactly the valve is the culprit because the spikes are observed exactly at the moments when the required oil pressure is increased (at that moment, the valve should close slightly). Obviously, the valve tends also to be stuck in an open position for a moment. Solution – replacement of the valve.
True, thou, I would suggest replacing the sensor too – it costs only EUR 50 (OEM), and, most probably, the existing one is full of dirt.
VANOS uses oil to turn the camshafts. If the oil pressure is not stable (and changes rapidly + unexpectedly) – it is logical that this hub is not working properly!

The second problem was even more cunning.

The owner of the car sent me a video of the cold start. Several videos. In all of them – the integrators were correct, and the mechanical efficiency of the cylinders was correct. Not a trace of any injector problems. Everything looks beautiful. And still… Overlooking the videos several times, in one of them, I noticed this:

Literally, for one second, the indication of the wideband probe of the second bank suddenly jumped from the correct 2.00V to 3.92V. And a second later – it went back to the correct value of 2.00V. Such (3.92V) indication means – there is only clean air in the exhaust. At the same time, as we see in the menu, the mechanical efficiency of cylinders No.2 and No.3 is correct. Obviously, they are working and burning fuel. Accordingly – it is not possible that there is only air in the exhaust!
There are no slightest doubts – the probe has a sporadic and well-hidden defect. In addition, at this moment, the defect manifests for such a short moment that DME even has no time to record the error message or react in any other way. Yes, the idle shivers for a moment, but that’s it – after a second, all INPA indications are perfect! Solution: replacement of the wideband probe of the second bank.
Here, two atypical defects can give quite strong headaches.