A nonlinear mean value engine model has been identified by using engine static maps. The model is linearized, simplified, and analyzed for the idle speed operating mode. Least-squares estimation of different types of input-output linear model are considered, with the aim to find a proper identification technique in the presence of significant speed perturbations of weakly excited engine. An analytical design method of tuning the PI and PID idle speed controllers is proposed. The method is based on the damping optimum criterion. Design of a more advanced, polynomial speed controller is also presented. The controllers are experimentally verified and compared.