As 250 says, a frayed cable can sometimes give intermittent stickiness, seemingly behaving ok for most of the time.
My old kit car used to love sticking the accelerator pedal open on full throttle once every couple of weeks. What that did for my middle-aged-racer credentials doesn't bear repeating - flooring her away from the lights followed by a massive scream of over-revving Pinto as the clutch was dipped for second gear - with the throttle remaining wide open...
I'd originally dismissed the cable as being guilty as it appeared smooth enough when tested by hand. But, frayed it was.
