In this research, we developed control solutions for the problem of precisely adjusting the fuel-to-air (FAR) ratio of a spark ignition internal combustion engine, using an adaptive control method of time-delay systems. The objective in FAR control is to maintain the in-cylinder FAR at a prescribed set point, determined primarily by the state of the three-way catalyst, so that the pollutants in the exhaust are removed with the highest efficiency. The FAR controller must also reject disturbances due to canister vapor purge and inaccuracies in air charge estimation and wall-wetting compensation. Two adaptive controller designs were considered. The first design was based on feed forward adaptation while the second design was based on both feedback and feed forward adaptation incorporating the recently developed Adaptive Posicast Controller (APC). Following successful simulation studies, experimental tests were conducted using vehicles provided by Ford Motor Company. Experimental results showed dramatic performance improvements with the proposed control solution over the development controller.