A couple months ago this was on the ground where I park at home. I originally thought it was just rotted foam that goes inside the bumper and kicked it aside. (I saw foam in my first XJ when I was in a collision) Anyway, I realized it was still on the ground and picked it up and realized it wasn't foam but actually hard plastic, maybe even stiff rubber. I want to guess it might have something to do with suspension as I've noticed its been a bit rough on the right side. If it is a car part, is it easy to replace at home for someone whose biggest DIY car work was a washer pump?

 

It's a bump stop for the rear suspension. There's one on each side that bolts to the frame rail above the axle to limit suspension compression.

 

Ah, sorry I didn't notice this reply. Thank you for answering. Just looked them up and it doesn't seem too complicated to install new ones.

 

I just read the first post, didn't realize it was from nearly 3 years ago, and was about to reply when I saw my old reply from 2018. Lol

Anyway, the rear bumpstops are easy to replace except that the mounting bolts like to snap when you try to get them out.