Method for identifying the thresholds at which pollutant gases are emitted with a view to controlling the operation in “stop and start” mode by stopping an engine just before and while a motor vehicle is stationary, whereby, upon each re-start, the amount of fuel injected is calculated, and the difference between the amount of fuel injected and the normal amount of fuel needed is calculated, the said resulting quantity being considered to represent the amount of fuel that was injected but not burnt; the said amount of fuel injected but not burnt is then compared against a predetermined threshold value, according to the distance covered, and finally, “stop and start” operation is or is not inhibited according to whether the said amount of fuel injected but not burnt is above or below the predetermined threshold value.