880 is too high for an '85 unless you've updated the chip. And yes that alone may cause the surging. Check the idle switch first, it's easy:
Then set your base idle to 800 with B-C jumpered, ignore the CO adjustment procedure here. Hopefully your base air/fuel mixture is already good, although if not that can cause surging too just as it can when vacuum leaks cause a lean mixture:
And if you want to test your ICV:
