engine "shimmys" at idle with AC on

[d9103365]

I have a 77 cordoba 400/4BBL. Whenever I'm at idle and the AC is on, the engine seems to shimmy a bit as if its struggling. This goes away once i start moving. It also seems to heat up a bit during this time, and oil pressure goes down....all of this corrects itself once I get moving. I've seen this problem on some of my other mopars before...what is the cause?

 

[Cava3r4]

sounds tune up related to me. Does your electric idle plunger work that is supposed to boost the engine RPM when you turn on the AC?