Erratic running 380SL
 

I have a very erratic running 1981 380SL. I am a mechanic but don't have access to the diagnostic tools to read the error codes.
Problems: -At idle will sometimes die, both hot and cold.
--At idle and while driving will sometimes race RPM up to about 2500. This happens both hot and cold.
-Oxygen sensor light is not lit.
- Engine power is normal
- Tune up is fine
I have spoken to the service manager at a local dealership. He was honest enough to admit that he doesn't have a mechanic that is really up on the older cars like mine, and thus is could become a very expensive problem isolation process. ( shotgun approach)