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Simultaneous control of speed and air-fuel ratio in a six-cylinder automobile engine is studied. A three-state engine model including rotational, air intake and fuel intake dynamics is used for control design. Control design focuses on application of nonlinear control techniques, specifically sliding mode control. Controllers are designed for tracking speed profiles and regulating air-fuel mixture. Multiple-surface sliding control is shown to result in good speed tracking in simulation and experiment. The production fuel controller and an observer-based sliding controller are shown to result in the best fuel control during speed transients. A standard sliding fuel controller is shown to result in high amplitude deviations due to oxygen sensor time delay. The best combination of controllers is shown to be the multiple-surface sliding speed controller and the observer-based fuel controller.