Can I save gas by leaving my car running?

My car has a 1.2L engine. If I run in to a store for 1-2 minutes should I leave my car on or will I save more gas by turning it off?

According to a local Public Service Announcement if you're going to be stopped for more than 30 seconds you should turn the engine off. Also you can never tell how long that clerk is going to take.Quite frankly the situation you described is a bad idea. Any delinquent that happened to be standing at the door of the store could hop in and take off. Why not he has the keys now, he has your address from the registration, and the keys to your house. Makes for a very expensive pack of cigarettes.

As a mechanic at the premier Caterpillar dealer in the U.S. I can tell you a fuel injected car with a V-8 uses less than a thimble-full of fuel to start up. The fuel system is pressurized and "gas" is always waiting at the injectors for start-up. Mid to late 80's and before had the carburated vehicles who's fuel system is not pressurized and after sitting a while air will enter the carb, travel down the line into the tank and require a longer start up time waiting for the fuel to go from the tank to the engine. Carb's aren't controlled as much and often a wasteful "gush" of fuel would come out on start up.

Turning off your car then re-starting uses renewable energy from your battery, mechanical energy from the starter, and makes a smaller "carbon footprint" . The wear and tear on the starting system and engine don't amount to more than $10 per year at best. My company spends over 10k a day just on fuel and everyone is required to shut off their company vehicle be it a semi or a small car anytime they are not going anywhere- even for a minute or two. As an F.Y.I. semi-trucks don't need to stay running for the "air brakes" to work. Air brakes have a reserve tank with built up air pressure whether the truck is on or off so when a driver presses the brake pedal air pressure pushes back the spring loaded brake shoes away from the brake drum allowing the vehicle to move. Google "hypermiling" for cool tips.