OBD problems, code P0442

Hello there, so I noticed few months ago the OBD drive cycle was not done it said one incomplete and I noticed it said catalyst, but a code every so often pops up like barely comes on but maybe once or two times a month. I clear it and check again few days later and same thing one incomplete. The light will not come on few weeks even like a month of so will not come on when it does I get the code of p0442 small EVAP leak. I changed the purge valve and reset the computer, then few days later checked the OBD said it had seven complete zero pending. So I thought purge valve fixed it, but I got the purge valve from a junk yard, so I do not know if the purge valve is the problem. I do not see any holes in hoses. I smoked it out. No leaks. I do not know what is wrong. P0442 and catalyst will not complete. Has rough idle, idles at 600 rpm then some times just drops to like 500 490 then back up to 600. It has brand new crank and cam sensors. Drives great runs good. I do not know what to do, lol.