Check the charcoal canister according to the manufacturer's specifications. A common problem with them is the leakage of one of the three ports. it is a plastic lid with a port and this lid is glued to the rest of the canister. A sponge with glue is used which eventually fails. It can be removed easily and glued with a better glue for plastics. The canister is on the passenger side of the engine bay, just behind the headlights assembly.
A hose is connected to this port from the throttle body housing which is under engine vacuum, thereby drawing air into the engine. Because the Mass air flow sensor is located just after the air filter, this extra air drawn into the engine is not measured.
The result is a lean air to fuel mixture with the adverse effects on engine life, overheating in the combustion chambers, pre ignition and poor fuel economy.