My Hyundai won't start in the cold

I have a 2002 Hyundai accent. When it gets below freezing the car won’t start and if I try to start it it floods the engine. I’ve already brought it to the mechanic and the dealer. They only things they have done is change the wiring. My friend has the same car and the same thing it happening to her. Can anyone tell me how to fix this problem?

They changed the wiring to what?
The spark plug wires? Wiring to the fuel pump?

What I would look at would be either the coolant temperature sensor, or the air temperature sensor as being the culprit.