Ah yes the fluctuating idle. I'm still working on my problem with it in my 85 turbo.
Here are the basic first steps. Vacum hoses should be checked for leaks. If they are the originals you might want to go ahead and change them now. Clean the throttle body. follow the directions in FAQ. Plugs & wires, cap& rotor. Also look for bad wires in the wire harness. C'mon fellow brick heads what else? Actually this is a common problem and you should find all sorts of info in the forum.
these are the first steps. Overall not to expensive and most of the stuff needs to get done anyway. Just keep crossing things off the list. Some day you will come across the fix ;-)