In this paper a novel framework for idle speed control of a spark ignition engine is introduced. The control task is to maintain the engine speed and the torque reserve at their reference values while the clutch is open. For this purpose a robust control design is proposed using sliding mode theory. It will be shown that this framework is robust against external load torque disturbances, parameter uncertainties and variations in the intake-to-torque-production delay leading to significant changes in the operating conditions of the engine. The performance and the robustness properties of the closed-loop system are demonstrated by nonlinear simulation and experimental results.