my car ('85 380 SE) "rocked" at idle.
I ran a can of "Techron" in a full tank of gas,
then changed the oil and filter.
the rock went away.(cleaned injectors)
It sounds as if you have a more severe problem,
I would pull and examine your spark plugs,
if one is fouled,check spark wires,cap,rotor,replace if necessary,check all vacume lines,look for disconnected lines,rotted lines(if you see this repalce all vacume lines)
this is the basics,after this checks out,its time to get a professional diagnosis.