Engine Misfire & Vibration: Causes & Fixes

Hello,
There are probably already posts on this topic, but I've been searching for a long time.
'I'm experiencing a problem where the engine runs very unevenly at idle. At speeds around 1200 RPM, the entire dashboard vibrates. Then it goes away until about 1600 RPM, where it becomes stronger again, and above 2000 RPM, it disappears. The rough acceleration is present across all RPM ranges.'
PD - The components are in order. The LMM (mass airflow sensor) is new, as are the air filter, diesel filter, and coolant temperature sensor. There are no error codes in the memory. As I said, this problem only occurs sporadically and only when the engine is warm. I've noticed that the problem doesn't occur when the outside temperature is around 0 degrees Celsius. The EGR (exhaust gas recirculation) system also seems to be okay. When I used to accelerate, there was always some soot, which was normal. That's hardly there anymore. The soot was more pronounced before. The diesel consumption has also decreased. Could it be that the intake air temperature sensor or the intake manifold pressure sensor is defective or providing incorrect values? But then there should be an error code in the memory, right?
I would be grateful for any help!

I completely forgot to include the engine specifications.
Golf4, 1.9 TDI PD, year 2000, 85 kW, 114,000 km.

Quote:

Could it be that the intake air temperature sensor or the intake manifold pressure sensor is defective or providing incorrect values?

But then there should be a stored error code, right?
No, as long as the incorrect values are within the acceptable range, no error will be detected. Therefore, it would be useful to read out and compare all the significant temperature sensors while the engine is cold.

Do you have a chip or a power box installed?

'No chip tuning or power box. I just drove it, and surprisingly, everything was fine again. And the current temperatures are above 5 degrees Celsius. It's incredibly frustrating! As I said, this damn problem only occurs sporadically. Even the technician at the last dealership couldn't figure it out. I'll go to another VW dealer later this week. What really surprises me is that the engine hardly produces any soot and that the diesel consumption is lower. Somehow, I think the engine is sometimes getting too little fuel.'
If anyone has any other suggestions, I would be very grateful.
Regards,
Robbin.