It is disclosed an engine evaluation unit comprising a microprocessor for receiving measurement signals from a gas flow control system of an internal combustion engine and for outputting a state signal indicating a state of the gas flow control system. The microprocessor provides input terminals for receiving the measuring signals as a first set of measurement signals before comprising at least one signal of a pressure upstream of a turbocharger and a signal of pressure downstream of a turbocharger. In addition, the microprocessor input ports provides for receiving a second set of measurement signals, which comprises at least one engine speed. The microprocessor is adapted to calculate a first set of prediction values by using a turbocharger model based on the first set of measurement signals, and the microprocessor is designed such that it comprises a second set of prediction values by using a nominal model based on the second set calculated by measuring signals. The microprocessor is also adapted to generate the aforementioned signal state based on a comparison of the first set of prediction values with the second set of prediction values.