While you have the intake off, rent a compression check kit to see if you have a dead cylinder. I am getting a rough idle, I swapped plugs out and still getting it. I pressurized the intake and tubing and found a leak at the base of my throttle body, also found #2 cylinder is week after the compression check.
I checked my radiator fluid and it was low, but my oil isn't milky. I am praying the head gasket isn't blown. If it is it will suck to pull everything and replace it.
I do hope your diagnosis isn't as bad as mine
.