oscillating idle, stalling
 

The other nite on my way home from work I noticed that my idle had started to oscillate and when I came to stops my cars rpms would drop so low that my car would stall. Have to blip the gas to keep it running so it don't stall. Also I noticed that when I take oil cap off my rpms would not change where before they would. Does this sound like a vacuum issue. If so how to diagnose? The had been running great to this point. The car is a 77, with 78 euro 3 liter. Any ideas, Thanks Jerry