Just a thought, looking at some of the screws/bolts on the throttle box there seems to be quite a bit of rust and corrosion. If any moisture has made it down into the gaps (which I think it may well have done) then you might be looking at seized components. Something like GT-85 or WD-40 squirted in and left to soak overnight might free things up or if that doesnt work a strip down and some heat applied may free everything up. As I said, just a thought.