Emission control is a very important issue in automotive engineering. In the urban trafic mode, the engine is known to be operated mostly in a transient state and the wide operating range and the inherent nonlinearities of the induction process make the design of the fuel-injection controller very difficult. In this paper, an observer-based nonlinear automotive fuel-injection controller is designed. The designed controller achieves excellent transient properties with a small chattering amplitude of air-to-fuel ratio. The controller is robust to model errors and the structure is simple enough to be implemented with on-line computation. The simulation results show that the control algorithm reduces the chattering magnitude considerably under the existence of modelling errors and a large measurement time delay.