Abstract: The ignition timing of a spark-ignited internal combustion engine is controlled to have a stabilized idle speed which is approximately equal to a desired idle speed. In accordance with the invention the engine is supplied with a fuel-air mixture which has a high air ratio, exceeding the air ratio corresponding to maximum mean indicated pressure and hence maximum torque. The air ratio is in a range wherein an increased air ratio corresponds to decreased mean indicated pressure and consequently decreased torque. According to the invention, the ignition timing of the engine is controlled to linearly advance the timing from a nominal retarded condition in proposition to change in engine speed below the desired speed. The timing advance has the same ratio to engine speed change as the ratio of nominal ignition pulse spacing to the desired engine idle speed.