Hi again.
the problem with my oscillating idle when cold came back. After replacing the water temperature sensor, the problem significantly improved right after the switch between petrol and gas but I have now oscillating idle later when the engine is almost warm and the temperature gauge is already at 3PM. It then goes away in a few minutes but I guess it will take longer when the winter comes.
The Prins guys tested the car for two days and say there is nothing to do and something must be wrong with the engine. The Volvo guys didn't even want to check saying if everything works on petrol, nothing is to be checked... They just gave up - my 850 is terminally ill
). But I haven't (can't) and now I am studying the principles of how the computer controls the injection and how the sensors influence the injection... I thoroughly and carefully cleaned the MAF sensor yesterday which also gives the information about the air temperature but the problem still persists. Oxygen sensor is now the only sensor that I haven't either cleaned or replaced. It is still the original one (17 years old). I will try to clean it.
Next, I will blow warm air in the air intake and see if this helps. If it does, than MAF sensor probably needs to be replaced. If the problem won't go away, I will have to think of a new strategy.
Maybe the ignition coil got weak...
I would very much appreciate any ideas what to do next...