Mono:
Apart from your current throttle/engine issue (which now sounds like a dodgy throttle cable or carb butterfly arm), you should really be using carb heat pretty much all the time at low power settings.
This is particularly relevant on approach to land...these small Continentals (up to the 6-pot O-300) have a different installation of the carb in relation to the oil sump, so are more prone to icing at lower power settings.
Personally, when operating my 65-powered machine, I use full carb heat from the commencement of the approach until shut down, and, like QNH1013, all the time when taxying on the ground before take-off, and then I only go to cold after full throttle has been applied.
Good luck, keep us posted.