Method of controlling the rotational speed of an internal combustion engine

A method of controlling the idling rotational speed of an internal combustion engine having an intake passage and a throttle valve in the intake passage, said method comprising the steps of:

• a. measuring the actual rotational speed of the engine and generating an actual speed signal corresponding thereto;
• b. detecting the temperature of the engine and generating a temperature signal that has a value corresponding to the detected temperature;
• c. generating, in response to the temperature signal, a reference speed signal having a value which is a function of the value of the temperature signal and which represents the desired idling rotational speed of the engine at the detected temperature;
• d. comparing the actual speed signal to the reference speed signal and generating a control output signal that corresponds to the flow rate of air drawn through the intake passage into the engine;
• e. restricting the value of the control output signal to be between upper and lower limits which are functions of the detected temperature of the engine;
• and
• f. controlling, in response to the restricted control output signal, the flow rate of air drawn into the engine through the intake passage to control the actual speed of the engine to reduce the magnitude of the difference between the actual speed signal and the reference speed signal.