Idle shake

it's not a balance issue. the thing would be rattling your fillings out.

i'm thinking you can tune your way to smooth-ness. or smoother-er.

it might be a "death by 1000 cuts" where you have just a little off here, a little off there and a little off elsewhere.

start with the basics: a comprehensive tune up. look for vacuum leaks. double check the mark on the balancer hasn't slipped. everything it tight, yadda yadda.