Abstract: An excess air control system and method (10) for a dual-fuel or spark ignition gas internal combustion engine (12) is provided. The controller (18) senses the exhaust temperature, senses the air manifold temperature, senses the air manifold pressure, and measures the engine power output of the engine (12). Based on these measurements and engine characterization data, a target air manifold pressure is computed. The target air manifold pressure is compared with the sensed air manifold pressure, and an air blowoff valve coupled to an air bypass line linking the air intake to the turbocharger (36) and the air manifold (40) is either opened or closed to achieve the target air manifold pressure.