Check your hoses from the purge valve and from the gas tank. More than likely you have a vacuum hose which has a leak. They do become brittle over time and need checking to be sure their not sucking air in, creating a code. Also, this hose could be at the tank,,,,which makes checking a little more difficult. Easy way to check a vacuum leak - spray the hoses with carb cleaner and see if the engine changes speed, at idle. Meaning the carb cleaner got sucked into the hose.