The flickering was tracked to be a bit corroded Ground.
I bought a bluetooth-based OBD reader named Drive Looper. It shows various data from the car's own system, focusing on mileage
For example, I drove 55Mph behind a semi, on a even road and the app showed a consumption of 59 US MPG! :O
Proof for my statement is that the average consumption showed on the app is about the same (+-0,25litres) i calculated using GPS-based kms instead of the car's own trip meter.
Bu it might be baloney what the temporary consumption is, the average MPG i get is 45.
Not bad for a russian car with a 30-years old engine design :3
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With Volvo to Valhalla and back!