E150 Accelerator Stuck After Cold Weather

When the weather gets down to about 15 degrees, my E150 Econoline 5.4 accelerator pedal is 'stuck'....so all I can do is drive at idle speed. After the engine warms up, the pedal becomes unstuck! I though it might be water in the accelerator pedal cable housing or perhaps the throttle assembly. Any ideas?

Flush it with WD40 and keep it lubed.