There are two major reasons why controlling spark ignition engines is a very difficult control problem: first, the parameters of the air/fuel mix feeding the engine are unpredictably (and drastically) fluctuating, and second, as many car owners know, the engine cycle is easily breakable, especially in the idle regime, when the engine sometimes suddenly stops. In mathematical terms, the first reason means that we do not know the exact values of the parameters of a system of equation that describes the engine's dynamics; we only know the intervals of possible values of these parameters, and these intervals are rather wide. The second reason means that the engine is a highly unstable system.
The authors apply methods from {\it robust control theory} (theory of control for systems with interval uncertainty) to verify the stability of a controlled Fiat Diedra spark ignition engine in the idle regime. As a result of this application, they verify that the proposed control guarantees stability (for all possible values of the parameters inside the given intervals). Thus, sudden engine stops are guaranteed to be avoided.
Previously known controls that guarantee the engine's stability require much higher fuel consumption than the tested control. Therefore, the fact that the new control is proven to be stabilizing, enables the car manufacturer to implement this new control, and thus, helps to save fuel.