Changed some parts but still wont start sometimes

[S4BiT]

So, my problem is, that my car wont start sometimes, it dont matter is it hot or cold. I have changed spark plugs and water temperature sensor (some guys in Audizine forum told that i must do that to fix it) but still same problems. Other problem is that on cold car dont idle at higher rpm-s (maximum 1100rpm or so). Someone had an idea? Computer dont find any faults. If these 2 problems caused by the same thing?