Method and system for operating a four-stroke multi-cylinder spark ignition combustion engine with cylinder deactivation

A method is provided for controlling a four-stroke multi-cylinder spark ignition combustion engine using cylinder deactivation of a subgroup of cylinders while another subgroup is working, during operation with an engine torque below a predetermined level. In that case, the method uses different techniques for deactivating some of the cylinders where one technique involves cylinder balancing for achieving stable operation and the other technique involves keeping the inlet and/or exhaust valves substantially closed during all four strokes. A system is also provided for implementing the above method, comprising a multi-cylinder spark ignition combustion engine with an electronic control unit (ECU), a fuel injector (114) and at least two throttles (106, 107), at least two chambers of an inlet manifold (108, 109) and means for disabling the inlet and exhaust valves for at least some of the cylinders.