1. A system for controlling engine air-fuel ratio entering an emission control device comprising: a switching exhaust gas sensor located upstream of the emission control device; a linear exhaust gas sensor located downstream of the emission control device; and a controller adjusting a fuel injection amount into the engine based on both said switching exhaust gas sensor and said linear exhaust gas sensor when operating near stoichiometry; and adjusting said fuel injection amount into the engine based on said linear exhaust gas sensor and independent of said switching exhaust gas sensor when operating away stoichiometry.