Abstract: An idling controller for a variable displacement engine which is capable of operating either in a partial-cylinder or an all-cylinder mode by varying the number of cylinders in operation. When the engine runs at idle, the idling controller assures optimum operation for either cylinder operating mode by varying the quantity of air intake according to the number of cylinders in operation, providing an improvement in both fuel mileage and strating performance, one or the other of which has had to be sacrified conventionally.

Abstract: In a multi-cylinder internal combustion engine having a plurality of cylinders which are supplied with air via one common throttle valve and a control unit for regulating the number of operating cylinders which suspends the operation of an arbitrary number of cylinders by intercepting the air supply to said cylinders, it is noted at a point the output of the engine under Z.sub.1 -cylinder operation coincides with the output under Z.sub.2 -cylinder operation at the same degree of opening of the throttle valve at a given constant rate of engine rotation. Based on such a fact, the multi-cylinder internal combustion engine is made capable of shifting to and from Z.sub.1 -cylinder operation and Z.sub.2 -cylinder operation in the proximity of said point where these outputs coincide. This way, there will be no fluctuation in the output nor shock at the time of switching, and the control unit for this purpose can be made simple in construction.

Abstract: In a multi-cylinder internal combustion engine having a plurality of cylinders which are supplied with air via one common throttle valve and a control unit for regulating the number of operating cylinders to rest an arbitrary number of cylinders by blocking the air supply to said cylinders, the output of the engine under Z.sub.1 -cylinder operation is known to come to coincide with the output under Z.sub.2 -cylinder operation at one point with the same degree of opening of the throttle valve under a given constant rate of the engine rotation. At such a point, the pressure of the intake manifold under both the Z.sub.1 -cylinder operation and the Z.sub.2 -cylinder operation remain at or close to a certain value respectively over a wider range of rotation of the engine. This multi-cylinder internal combustion engine enables smooth switching between the Z.sub.1 -cylinder operation and the Z.sub.