This paper is concerned with the VGT (Variable Geometry Turbocharger) and EGR (Exhaust Gas Recirculation) control design for the air path of a Diesel engine. The purpose is to validate a Diesel engine model by choosing the right operating conditions based on a series of open-loop tests. For the control design, an observer-based control with integrator is developed for the estimation of the compressor power and a good tracking of reference pressure signals which correspond to emission standards. The efficiency of this method is illustrated through simulation results on the Amesim software.