I recently did some work on my throttle body (had it removed, cleaned all the valves, etc.) and after I put it back together I noticed something strange. Every once in a while, after the car has been stopped for a minute (so when leaving the garage or after waiting at a red light, etc.) the throttle gets stuck on idle, and I have to push really hard on the pedal to get it to unstick. I did some looking around and I noticed two things: the problem is not in the cable, the throttle plate assembly is somehow stuck, either inside or outside the throttle body; once I unstick it I cannot get it stuck again by hand, no matter how hard I try. The only way to replicate the issue is to drive around until it happens. What could be causing this?
Is the car running when you try to "get it stuck again by hand"? If not, remember that when the car is running with the throttle closed, there is vacuum being pulled against the throttle butteryfly by the running engine.
Perhaps there's some play in the pivot or the assembly that allows the intake vacuum to pull the butterfly into a position where it binds. If the car isn't running while you're manipulating the throttle by hand, the assembly may not "suck" itself into the "stuck" position.