Most early and even later Renix 4.0s could be bothered by excessive oil in the air cleaner box.
A fix from my old days as Service Manager at a Jeep dealership follows. Information was provided to me from a buddy at JeepTech during those days. I don’t believe it ever came out in a Technical Service Bulletin.
Remove the valve cover and turn it over. Next, remove the fluted tubes that are now facing you by removing three screws on each.
Clean and de-burr/sand all rough edges nicely, clean with solvent, and reinstall. Don’t be concerned about the chintzy gaskets that will probably crumble into oblivion when you remove the fluted tubes. They can go back together without gaskets.
Here’s a handy video from my friend Brendan showing more detail.