Seems like the cable might be rusted tight. Take it off the 'ped and see if you can slide the cable up and down in the tube. try lubing it with penetrating oil and one of those gadgets they use on bike cables. If it's still stuck, I'd have to recommend a new one.
On the other hand, (It'll be obvious on inspection) the outer tube the cable slides in may have worn away in parts, or has come free somewhere along the line. this can affect how it pulls quite a bit.