I was having similarly annoying issues with my 1800 Sportswagon (EA81). It wouldn't stay in tune and idled too fast. The best thing I ever did with this car is acid-bath the carby. It turned the thing from sounding (and jumping around) like it had an old lawn mower engine under the bonnet into something that sounded like it was ready to rally.
Acid bathing the carburettor removes all the built up carbon that is clogging it and choking it up. It really turned my machine into something that sounded comparatively brand new, and I can't recommend it enough.
I'm in Melbourne, so I used Wilson Carburettor Service in Airport West. John is a genius. I watched him work on the carby on my old Kingswood the day I met him and the thing just fell apart in his hands, and then fell together again just as quickly (once he'd blown the bit of gasket out of the bulb, which had been causing havoc). Nice fella too.
