A system includes an internal combustion ignition engine with an exhaust gas flow, a particulate filter in the exhaust gas flow, a NOx reduction catalyst in the exhaust gas flow downstream of the particulate filter, a first oxygen sensor coupled to the exhaust gas flow downstream of the NOx reduction catalyst, and a second oxygen sensor coupled to the exhaust gas flow between the particulate filter and the NOx reduction catalyst. A controller includes an exhaust conditions module that interprets a first oxygen signal from the first oxygen sensor and a second oxygen signal from the second oxygen sensor and a combustion control module that commands a high engine-out air-fuel ratio when the first oxygen signal indicates a low oxygen content and commands a low engine-out air-fuel ratio when the first oxygen signal indicates a high oxygen content.