How much gas does idleing save?

Answer 1

Idling modern electronically fuel injected cars does not save gas, it wastes it. Back in the days of carburetors, cars wasted a bit of fuel while starting up since the carburetors dispensed way too much gas during the start-up process. Each start up of old carbureted cars used the same amount of gas as 1-2 minutes of idling, so you saved gas by keeping your car running instead of shutting it down at short stops.

The only rare advantage to idling a modern car is in cold weather when the engine is still below normal operating temperature. In those cases, the few pennies of gas will cost you less than the cost of wear and tear caused by starting a cold engine.