intense vibration at idle (617) Help?

[klataklatacoupe]

I have an '84 300cdt. Since i have had it, it has always run good and smooth except When it needed a rack damper adjustment and even then it was just a slight "wobble" at idle. Recently, it has developed an intense vibration when at idle speed. Strong enough to shake the hood, bumper, steering wheel, the corner lenses actually shook loose, etc. With 310,000 mi. on it, i'm not sure where to begin. any input would be very much appreciated.