Embodiments for controlling exhaust air-fuel ratio are provided. In one example, an engine method comprises adjusting upstream exhaust air-fuel ratio to maintain a first emission control device at or below a threshold temperature, and when the upstream exhaust air-fuel ratio is below a threshold, injecting air into an exhaust passage between the first emission control device and a second emission control device to maintain downstream exhaust at a different, higher air-fuel ratio. In this way, excess emissions may be converted while maintaining the emission control devices below a maximum temperature.