Hello guys,

I've opened two threads on this matter, received many suggestions, and then I found the solution.
You might have this same problem if your petrol sits in the car's tank for long periods of time.



Short version:
If you have a (turbocharged) petrol engine, and it doesn't start well, first thing first recharge your battery and search for a fuel station that sells 95/98 octane petrol on very very high quantity.
Don't use any special fuel (Shell v-power, high octane stuff, etc) unless you really need it.
I've discovered myself that these fuels, due to the fact that they are not sold in huge quantity, tend to become old in the fuel station tanks.

So they tend to ignite with more difficult.


Long version:
To solve my rough starts in the morning, I've put in the tank a special fuel sold here (blupower), thinking that additives can do something to improve my ignition; same as before, probably worse; then I've changed the air filter, spark plugs, oil an oil filter (jobs that I had to do anyway): no improvement;
Then I've searched for a really busy fuel station and put in some normal petrol, suitable for my car.
Next morning, perfect start; since then, perfect starts every morning, even in the coldest months of the year.

Here is the link to my specific case:

https://www.fiatforum.com/tech-talk/463677-injector-cleaner-you-know-works.html