The present invention overcomes these problems by providing an oxygen sensor located in the exhaust stream of an internal combustion engine, a load sensing device which generates a signal indicative of an internal combustion engine load, a central processing unit which calculates a running average of the oxygen content in the exhaust stream indicated by the oxygen sensor and a fuel injection device which supplies fuel to the combustion air in response to the central processing unit. The central processing unit uses the running average of the oxygen content in the exhaust stream, in lieu of the instantaneous oxygen content, to modify the fuel equation for determining the proper air fuel mix when transitioning from closed to open loop operation. The resulting air fuel mixture thus reflects the average oxygen value in the exhaust over a period of time. This average serves to cancel out the extreme surplus and deficiency of oxygen in the exhaust stream due to dithering.