Unless your car looks like this, (or even if it does), you should NOT let your car IDLE for extended periods of time trying to "WARM IT UP". According to most Master Mechanics, letting your car idle for longer than 5 mins, or the time it takes you to scrape the ice off of the windshield, actually does MORE DAMAGE to your car.

The idea of warming up a car by idling comes from a time long ago when cars were built with carburetors in the engine instead of fuel injectors like most cars built after 1990. It has to do with the gas and air mixture reaching proper operating temperature. But the invention of fuel injectors and on-board computers that automatically regulate the mixing makes 'idling' a car to warm it up obsolete.

Modern cars are designed to be warmed up while being driven so basically all the owner has to do in get in and drive. Idling not only wastes gas and oil, and is bad for the environment, it causes unnecessary wear and tear on pistons and cylinders and can cause and engine to wear down prematurely.

So if your car was built AFTER 1990 and doesn't have a carburetor, don't waste time and gas with excessive idling, just get in and go...