Explanation:

Idling refers to running a vehicle's engine when the vehicle is not in motion. This commonly occurs when drivers are stopped at a red light, waiting while parked outside a business or residence, or otherwise stationary with the engine running. When idling, the engine runs without any loads except the engine accessories. Idling refers to running a vehicle's engine when the vehicle is not in motion. It is estimated that Idle running left the maximum CO in the exhaust.