Rough Idle when at Stop light 560SL please HELP

[digidan]

So we got a sweet deal on a beautiful red 89 560 SL and have had such a great time with it. Recently I've noticed a problem and its slowly starting to get more pronounced. When you start it the car usually runs great, but a month or so ago the car started to feel as if it was running rough in almost a rythmic fashion. Its most noticable when at a stop light after driving for a bit, every few seconds the car's idle cycles down and the oil gague jumps all over the place. It almost feels like the car wants to turn off its not that deep of a jump in the idle but it is quite annoying. I've been reading online forums but would like to know where I should start. Most of these say to look at spark plugs and such but was hoping to get some knowledge as this seems to be a great community of MB owners. Thanks in advance for your help!