Routine Order

Idling: Myths Versus Reality
Contrary to popular belief, idling isn’t an effective way to warm up your vehicle, even in cold weather. The best way to warm it up is to drive it.

The article also says that you can save a lot of fuel by turning it off if you are going to be idling for more than 10 seconds. 10 seconds is the time below which restarting your car will consume more fuel that letting it idle.

I have always known, in the depths of my brain that idling a car immediately after starting it in the morning does nothing to help prolong the life of the engine. With modern electronic computer-controlled engines, you would think the engineers thought of the cold starting problem - and they have!