Kerry, I would soak it longer, up to a week if necessary. Take it out of the solution every day, blow it off with compressed air, and try to work the throttle shaft. Put it back in and repeat. The operative word is patience.
I don't know if Berryman's is the right stuff for this, by the way; I'm not familiar with that stuff. Is it just a solvent, or is it also a lubricant like WD-40? You need a penetrating oil of some sort for that job. If the Berryman's doesn't work after a while try WD-40 instead.
Last option would be heat, and I don't mean a torch. Try just putting it in the oven at 300 for 15 minutes or so, and then see if you can work it loose when you pull it out. Heat will expand the components, and help the frozen parts break loose.
Hope that helps - Jay