Car won't start up when cold outside - 1999 Ford Taurus

My first thought you say when it is hot outside it will not even crank or do anything. I assume you do nothing and it will crank when it is cold. Well if that is the case I am thinking it may be a loose connection. Metal will expand in heat and contract in cold. My crazy thought is a connection is tight in cold and loose in heat. In heat try moving the battery, ground, solenoid connections if loose tighten them up.
If the car does try to crank
IAT sensor may have something to do with it(intake air temperature) link below
https://www.youtube.com/watch?v=NVIRlpTj-Gk

If check engine light is on have codes checked. Most auto part store where I live will check codes for free.

have you checked for spark? it has been my experience that most chevys have a problem with electrical stuff when cold. i would check for spark, it may be present but weak. i have a 95 k1500 suburban, and things like window motors and seat motors lag alot when its cold outside. if spark is weak, u may need a new coil

ignition coil

it often happens in the winter, naturally, the cold weather will have some effect on all the car's system, especially the battery and cooling system.
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Easy to get a MST-3

I personaly would replace the sensor

The next time it won't start check the fuel pressure, bet there is none.

Sounds like you might have a faulty ignition switch and ignition lock cylinder.These cars are known for the ignition switches getting hot and then they won't start.

well if you live some where where its cold and you didnt plug it that probably why but if not maybe your alternator is broken or your gas line might be frozen if its cold outside. good luck

my truck won't start when it's cold outside. but when it's warm it start's right up I changed the oil and filter and the battery is new what's wrong.

Adjust choke assembly. Good mechanic, 5-10 min.