I had those two codes when i bought my xj8 a month ago. I cleared the codes a couple times, but it would always come back at 3/4 of a tank. So i checked out the purge valve (purge canister) and it had no holes in the hoses, the hoses looked new actually. Then i grabbed the green cap and noticed it wasnt screwed on tight. So i tightened it and now after driving for 3/4 of a tank the light hasnt come back.

So if you have those codes, you just might have a slightly unscrewed green cap. Im guessing its a pressure release valve, its the green one that says "hand tighten only".
Good luck, cheers!