What's the ratio of air to petrol in gasoline engine when the car is idle?

The air to petrol ratio in a gasoline engine when the car is idle typically ranges from 14:1 to 16:1. This means that for every 14 to 16 parts of air, there is 1 part of petrol (or fuel) being mixed in the engine for combustion. The specific ratio may vary depending on the engine design and other factors.