Method of monitoring an engine able to operate with selective valve deactivation

A method of monitoring the operation of intake valves of an internal combustion engine, where at least one or more cylinders of said engine have more than one intake valve, and adapted to operate in different modes where at least one of said intake valves for a particular cylinder can be selectively activated, or de-activated so as not to open during a firing sequence for the particular cylinder comprising:

• a) monitoring intake manifold air pressure;
• b) during a time window with respect to an intake phase for said particular cylinder, determining a condition of whether the intake manifold air pressure drops by a threshold or to a particular threshold level;
• and
• c) determining functionality of the intake valves dependent on the outcome of step b);
• where said method is implemented during a mode when at least one intake valve is controlled to be activated for said particular cylinder and at least one intake valve is controlled to be deactivated during respective intake phase for that cylinder;
• and
• where if the condition of step b) is fulfilled, step c) comprises determining that the engine is operating correctly and/or if the condition of step b) is not fulfilled, step c) comprises indicating a fault.