Questions on driving: an extra step on gas before shutting down the engine?
 

I've been watching some Japanese car video this weekend. Seems like they step on the gas once more before shutting down the engine... What's going on there?

That is one thing you do not want to do before shutting your engine off, you will ruin your sparkplugs, and cause more of ignition problems to your car.

The extra unburnt gas can wash the oil off you cylinders, it can foul your spark plugs, and it can plug your cat.

I think that this is useful for older cars with carborators.