Various methods and systems are provided for adjusting an air-fuel ratio for combustion in an engine. In one embodiment, a method for an engine (e.g., a method for controlling an engine system) comprises responding to a sensed change in a load on the engine, or indications of engine knock or misfire, by one or more of: altering a speed of the engine, adjusting a fueling flow rate into at least one cylinder of the engine, and adjusting a position of a valve in a bypass passage configured to direct compressed intake air away from cylinders of the engine to obtain a determined air-fuel ratio; and thereby maintaining an air-fuel ratio in a determined range.