Mercedes-Benz GL550 Gas pedal is stuck Inspection at your home or office.

Assuming the linkage between the throttle pedal and the engine is unobstructed (something you can check visually by checking around the gas pedal or floor mat for foreign objects that may be obstructing the path of the gas pedal), a sticky gas pedal is almost always due to accumulation of unwanted goo at the throttle body. This makes the action of opening and closing the throttle a notchy, imprecise operation.