The commercial pilot stated that he was practicing an Instrument Landing System (ILS) approach with his flight instructor/passenger. While on the glideslope, he attempted to add power, but noted no response from the engine. The engine revolutions per minute (rpm) remained at 1600. The pilot declared an emergency with the air traffic control tower, and began looking for an alternate off field landing site. Once located, he landed on a hill, substantially damaging the wings and landing gear. Postaccident examination by a Federal Aviation Administration inspector revealed that the throttle cable had come loose from the arm on the fuel servo. A review of the airplane's maintenance records found that the airplane had undergone an engine change 32 hours prior to the accident.