Abstract: Methods and systems of recirculating exhaust gas in internal combustion engines are disclosed. An internal combustion engine includes a set of cylinders, an intake system disposed in fluid providing communication with the set of cylinders, an exhaust system disposed in fluid exchanging communication with the set of cylinders, and a controller. In response to a detected recirculation condition, the controller prevents fluid communication between the intake system and a subset of the set of cylinders and recirculates exhaust gas between the subset of the set of cylinders and the exhaust system.

Abstract: Methods and systems are provided for addressing spark plug soot fouling. In one example, a method may include alternating one or more combustion events with spark timing advanced with one or more combustion events with nominal spark timing. The approach allows spark plug over-heating, and related issues such as knock, to be reduced.

Abstract: A method is disclosed for controlling operation of an engine coupled to an exhaust treatment catalyst. Under predetermined conditions, the method operates an engine with a first group of cylinders combusting a lean air/fuel mixture and a second group of cylinders pumping air only (i.e., without fuel injection). In addition, the engine control method also provides the following features in combination with the above-described split air/lean mode: idle speed control, sensor diagnostics, air/fuel ratio control, adaptive learning, fuel vapor purging, catalyst temperature estimation, default operation, and exhaust gas and emission control device temperature control. In addition, the engine control method also changes to combusting in all cylinders under preselected operating conditions such as fuel vapor purging, manifold vacuum control, and purging of stored oxidants in an emission control device.