Fractured

Hello everyone, Long time lurker buy decided it was time to make a post. I own a 2000 XJ and am having a hard time tracking down a misfire.

The misfire is very slight and only noticeable at idle. It doesnt throw any codes and the computer has none stored. When it is missing i can very slightly notice the rpms dipping up and down, maybe about 50 rpms.

I have checked the head and head gasket, both are good and no leaks or cracks. I have done plugs, cleaned IAC, ran fuel injection cleaner, as well as seafoam.

Thats where it gets weird for me. If i run seafoam through it and smoke my neighborhood out, it runs 100% for about three days. Then it seems to come back. I originally thought about rings but not if it runs good for 3-4 days. So im stuck. I do want to replace some things (cps, tps, coils) so im not too upset but id like to get it figured out.

Any thoughts?