The invention relates to a waste gas probe which is disposed in an internal combustion engine, comprising a plurality of cylinders and injection valves associated with the cylinders, in order to measure fuel. The waste gas probe is arranged in a waste gas tract and the measuring signal thereof is characteristic for the air/fuel ratio in the respective cylinder. The measuring signal is detected in relation to a reference position of the piston of the respective cylinder at a predefined crankshaft angle and associated with a respective cylinder. A manipulated variable which is used to influence the air/fuel ration in the respective cylinder according to the measuring signal detected for the respective cylinder is produced by a controller. The predefined crankshaft angle is adapted according to an instability criterion of the controller.