This paper presents a methodology of robust control applied on a nonlinear MIMO system, on the air path of a turbocharged diesel engine. The methodology consists in first analyzing the MIMO system to observe dynamic properties with several tools, i.e. condition number, relative gain array and Gershgorin bands, before designing the controller. Hence, a sequential robust controller synthesis is proposed to obtain a decentralized control taking into account coupling and uncertainties of the nonlinear system. The results obtained from a Mean Value Engine Model (MVEM) engine simulation model show the real time applicability of the proposed method and the good control performances (good response time, no steady state error) for various engine speeds.