1. A method for regulating the ratio between air and fuel during combustion in an internal combustion engine, comprising: providing fuel in a tank, wherein at least one of the quantity of the fuel and the quantity of the air is adjusted such that a desired air/fuel ratio is achieved, wherein to check the air/fuel ratio a lambda probe is provided in the exhaust gas of the internal combustion engine, using a lambda signal from the lambda probe to evaluate and regulate the air/fuel ratio, performing the regulation as a function of an adaptation value for the quality of the fuel and with the aid of a regulation value for the air/fuel ratio, adjusting the adaptation value after the tank is filled on the basis of a deviation from a target signal occurring in the lambda signal, such that the lambda signal again corresponds to the target signal, and determining the adaptation value as a function of the previous adaptation value and as a function of a correction factor.