Patent ID: 7503320

Claim:
A method for operating an internal combustion engine ( 1 ) at idle speed ( 47 ), the engine ( 1 ) being equipped with a purge device ( 28 ) comprising a purge valve ( 31 ) for purging a fuel vapor canister communicating, via a vapor pipeline, with an air inlet manifold ( 5 ) of the engine ( 1 ) in order to recirculate at least some of these vapors thereto when the valve ( 31 ) is open, in which method an idle speed controller (ISC, 47 ) acts upon the idle speed of the engine, and including in particular the following steps: i) a command to open the purge valve ( 31 ) is issued, ii) the idle speed controller (ISC, 47 ) is operated using a PID controller ( 49 ) that has proportional ( 53 ), derivative ( 55 ) and integral ( 51 ) functions to cause it to act upon said engine idle speed without causing any appreciable variation in this speed in spite of the fact that the purge valve is open, iii) the data supplied to the engine control unit (ECU, PCM, 25 ) by the PID controller ( 49 ) is analyzed, and this data analysis is used to provide diagnostics information regarding the operation of at least one of the purge device ( 28 ) and said purge valve ( 31 ), characterized in that said analysis comprises analyzing the change in the integral function in order to diagnose whether the purge device ( 28 ) is operating correctly.