As you mentioned in your post - these rough idle issues are indeed very elusive. Still from reading your post I would consider doing the following before getting rid of the car or setting it on fire..
Clean the idle control valve and replace both hoses leading to & from it if they are dry and brittle (most likely).
Replace the plug wire set if this has not been done in recent years. If you search under my name you will find details on doing just that.good luck