Idling with very minor speed variation

[ls5czu]

My A2 ABY idle with very little speed differences of approx. 40 rpm ever approx. 10 seconds. It's hardly to feel. I have replaced:

- air mass sensor
- fuel jets
- Spark plugs
- ignition coils and amplifiers
- idling valve
- fuel pressure regulator
- checked for air leaks, all good
- disconnected pvc and fuel tank ventilation
- checked with a different OEM mcu

Any further ideas?
Emission values are slightly above limits when idle speed varies.

[Tractor Dave]

Have you tried another lamda sensor?

[ls5czu]

Yes, i forgot to mention. Lambda also new.

[Tractor Dave]

Sounds like you have done pretty much everything. I'm just wondering if your fan circuit or air conditioning is kicking in momentarily and effecting idle? Also check your alternator voltage while this is happening.

[ls5czu]

Yes, this i checked...fan and ac off. Battery voltage is also slightly changing...this i would expect by the rpm change...i could take off the belts of alternator and hydraulic pumup.ä, as last try...but i'm skeptical.