If your idle used to be fine then it could be the loose throttle plate issue, or it might just be the colder winter air. Colder air is denser and so needs more fuel to maintain the correct fuel\air ratio. I have to adjust most of my gassers for seasonal changes. Have you tried richening the low end? Or it could be that you need to do a carb rebuild - if you haven't done that in four years then you probably do need it. The pumps \ membranes loose elesticity over time (due to the methanol in gas), so don't perform as they used to. If you haven't done it it's very easy. The kits themslves are around $8. I believe the kit for this carb is the Walbro K20. Lots of useful videos on Youtube. While you're at it you might as well check the tubing inside your tank. Tygon usually stiffens after 2 seasons.