Car starts great when really, really cold

Cars always been hard to start since purchased 2 years ago. Type of gas has a dramatic effect on how it starts and performs; Shell is all it wants to burn. I refuse to believe that this is normal... for any vehicle. After several attempts to cure the problem, complete tune-up, new wires, injectors, distributor etc, ect, ect.....I've finally noticed that when it is extremely cold, say -25 deg Celsius (and the cars been outside for awhile, 2 hrs) it starts like a charm, no hesitation, first crank, immediate start. Completely unlike any other time in starting the vehicle, other than if you have just shut it off within 10 minutes. Did not know this because it's always been garage parked. Read and researched numerous posts to try and figure this problem out, seems there's are lot of solutions. Based on my findings with the low vehicle temperature situation, would any of you readers be inclined to believe that it may be my coolant temp sensor problemm, and when it is finally cold enough, it gives the correct signal for fuel mixture...

Comments please...