How do you fix a 1980 Cadillac Eldorado 5.7L that does not start in cold weather except inside a heated garage?

The choke on the carberator is stuck open so it allows too much air for the amount of fuel needed to start the car. If you look in the top of the carb, there is a flap that is probably stuck straight up and down. In cold weather, that flap is supposed to be sideways and closing off the opening of the carb.

Expanding on the above answer, while warming up, this choke flap is controlled by an electrically heated coil (automatic choke), this sits on the side of carb and is about 2" in circumference. It has two screws holding the face of the thing in position. When loosened, the face can be rotated to adjust the coil inside/level of choke, there are marks to show the normal position as a reference.

This will get the engine started in the cold, but is probably compensating for some other problem, and may make engine run rich once warm.

Steve