Abnormality diagnosis apparatus for evaporative fuel processing system

An abnormality diagnosis apparatus for performing a leak check and for determining whether or not a leak exists in an evaporative fuel processing system which includes a fuel tank, a canister for storing evaporative fuel generated in said fuel tank, a charging passage for connecting said fuel tank to said canister, a purging passage for connecting said canister to an intake system of an internal combustion engine, and a purge control valve provided in said purging passage, said abnormality diagnosis apparatus comprising:

• a pressure sensor for detecting a pressure in said evaporative fuel processing system;
• pressure reduction processing means for executing a process of reducing the pressure in said evaporative fuel processing system with a limited flow rate of gases passing through said purge control valve when performing the leak check in an idling condition of said engine,
• wherein said limited flow rate being set to a value equal to or smaller than a predetermined flow rate which is smaller than the maximum flow rate applied to the leak check performed in operating conditions of said engine other than the idling condition;
• and
• leak determining means for performing the leak check on the basis of a change in the pressure in said evaporative fuel processing system after the pressure reduction process.