Comic resonance oscillation at idle

Hello!
I'm having the following problem with my 1994 Golf 3 TDI:
There's some kind of resonance vibration when the engine is idling. It's definitely coming from the engine! It sounds like the idle speed is fluctuating. But the tachometer needle is completely steady, so it can't be fluctuations in the engine speed. Do you have any idea what this could be? This vibration is really annoying.
Is a 1Z engine with 210,000 km a good thing?

Regards,
Thomas.

Hello,

Let's read out measurement block 13 from the engine control unit and post the values.

Hello!
What is measurement block 13?
Does it cost anything at VW if I have the control unit read out?
And what values are stored in this block?

Regards,
Thomas.

Hello,

Normally, that costs something. But you never know...
A list of the measurement data blocks can be found in the error database.
Okay, since you're already at VW, why don't you have the diagnostic trouble codes read?