I don't have the answer but I tend to think it's a moisture problem, particularly, with respect to the gas cap. Or, perhaps your evap needs to dry out or has, over the years, become contaminated.
I've had the issue in my '02 WJ, on and off, and that's what leads me to my thoughts. Sometimes it goes away, with concurrent weather changes, and once I replaced the cap. Replacing the cap didn't fix it regardless what the code(s) said.
When parked for extended periods, keeping the tank full seems to help/alleviate the issue.
Last edited by funfred; 02-18-2019 at 12:47 PM.