[unclesol]

Congrats on the new addition!
I recently picked up an 84 Carrera that had a very similar idea surging issue. Long story short, my issue turned out to be a leaking left-side intake valve cover gasket, that was creating a major vacuum leak. Also didn't help that the PO had disconnected the O2 sensor, so the computer was not getting the necessary feedback.
All new valve cover gaskets, and a valve adjustment later, it runs like aSswiss watch now.
I hope this helps!