As long as you give us the feeling that you appreciate and use our comments: of course!
Diesel, no mixture, just injection of given quantity of fuel at a given moment. Too cold measured temperature would give hard running engine and higher idle rpm.
As said, symptoms could relate to the temperature sensor, which is a cheap and "easy" fix. Now that you excluded this one, you know what you might be up to. BTW, just a thought: I think that 206Tkm is rather young for serious engine trouble and fairly low for a 16+ years old diesel car. Are you sure about the mileage?