Lately I have been noticing a pretty rough idle in my 01 xj with 99k miles. I recently replaced the head (cracked) and after putting in an oversized oil filter and 10w-40 I have 10 psi at idle, which I am fine with, but it seems to get rough sometimes. When I pull up to a light at hot idle I would say about 50 percent of the time it idles rough, the rest of the time it seems smooth. But when it's rough, it gets rough enough to feel it in the seat and see the mirrors shake. This is the part that worries me so I'm wondering what could cause this intermittent rough idle. Just the bearings? IAC? Timing sensors? Any input is appreciated.

 

I have this problem from time to time myself....just not as often. Sorry I couldn't help more but at least you'll be bumped back to the top where more experienced members may see it.

 

Possible low idle. Next time it happens, raise your idle slightly and see if it smooths out.
Are your plug wires away from any metal contact?
Have you done a compression check?