Engine Smoke: Troubleshooting High RPM Startup

hello

Yes, I used the search function, but I didn't find anything useful that could help me.

Regarding my problem, and possibly yours as well:
My 1996 Passat, with the AFN engine, has 165,000 km (approximately 102,000 miles) and has been exhibiting some unusual smoke in the 2500-3000 RPM range during constant speed driving, especially when the engine is warming up.
'That is, I maintain a constant speed while driving. As soon as I reach the temperature range (according to the display) of 70-90°C and drive at a constant speed for a period of at least one minute, my car starts to emit smoke like a fog machine. The smoke is white-blue, and when the window is open, it smells strongly of diesel fumes.'
'As soon as I reach 90°C and the engine is running at a constant speed again, the problem no longer occurs. The smoking also completely disappears when I change the engine speed or drive below 2500 RPM or above 3000 RPM.'
In addition to the smoking, I'm noticing another issue with the engine – a kind of jerking or stuttering.
The car otherwise drives normally, and the oil consumption is a maximum of 1/2 liter over 5000 km.

I also once did a test drive with the 10c tuning enabled, but the effect didn't occur then. However, I suspect that the engine wasn't cooled down enough beforehand.
Based on the excessive smoke, I suspect an over-injection or incorrect fuel injection. Could it be that the temperature sensor for the engine control unit is defective, since the effect only occurs within a specific temperature range? I'm ruling out mechanical engine damage, such as valve stem seals, connecting rod bearings, or head gasket.
There used to be a similar thread, which I a) can no longer find and b) didn't yield any results at the time.

I would appreciate any suggestions!

ixery

ixery wrote:

There used to be a similar thread, which I a) can no longer find and b) didn't yield any results at the time.

Hi.

more than is stated here.

/viewtopic.php?t=1790&highlight=resonance

I don't know either.

@ulf: Thanks for the link.

Yesterday, I made several attempts to better determine the timing and duration of the issue. I observed that it doesn't smoke when: a) I engage the cruise control at the specified RPM and corresponding speed, b) the '10c tuning' is activated, and c) the outside temperature is below zero.
I experienced the smoking issue when the outside temperature was between 5-8°C.

It also seems to me that the assumption regarding resonances and the ECM's feedback control is quite fitting and plausible. Furthermore, if a relatively coarse grid is used and the jumps between values are unfavorable for such a situation, it definitely makes sense.

ixery