Can someone tell me if there is a way to narrow down the problem? It shows no CEL at the moment. I do remember headlights "pulsating" at idle in the past but wife changed bulbs and dont know if still present (im deployed so cant check).

Things I suspect:
1) Coil Packs (no cell showing)
2) Alternator (maybe regulator is going bad and affecting idle and I think that sits inside alternator)
3)Valve adjustment


Car has 185K miles and automatic.

 

Maybe just a loose or leak in your vacuum lines somewhere if this is just happening on idle.
Not an expert, just some thoughts and virtual troubleshooting:
(1) going bad I would think would cause misfire or hesitation when accelerating.
(2) going bad would affect your lights and so would a battery or charging system going bad. Don't think it would cause rough idle though.
(1) and/or (3) would affect more than just your idle and eventually light up your CEL I would think.

Hopefully the experts here will chime in...

 

With that many miles and if they haven't been changed prior to this I would start with the plugs, then coilpacks, for sure valve adjustment if we are talking about engine shake not lights dimming.

Thanks for your service lets us know if we can help out.