This is a fairly commonly reported problem.  The throttle will stick, usually after cruising in fourth or fifth gear.  The sticking point is shown here, under the hood, part of the throttle body linkage.

The metal pipe in the left side of the red oval next to the linkage works its way out and starts binding the linkage.  Push the metal tube back in place.

A friend of mine used a zip tie to keep the tube in place.  A more permanent solution would be to use some JB Weld adhesive.