Abstract: A method is described for monitoring the air/fuel ratio in an internal combustion engine by means of the measurement of pressure variations in the induction duct of the engine and for indicating appropriate changes in the fuel supply, in a closed loop, to return the ratio to the desired value. This method is achieved by means of a device which is characterized in that it includes a pressure sensor, means for processing the signal obtained from the sensor and a microcomputer for checking whether or not the values processed by said means fall within a predetermined, previously stored range found experimentally on a test engine under proper combustion conditions. If the processed values are outside this range, the microcomputer activates an alarm signal and/or operates, directly or indirectly a device which adjusts the air/fuel ratio to return it to normal values.