On July 5, 2017, about 1440 eastern daylight time, a Piper PA-32-300 airplane, N112DE, performed a forced landing near Rushville, Indiana. The airline transport-rated pilot and two passengers were not injured, and the airplane was substantially damaged. The airplane was registered to Four Aces Escardrille LLC and operated by a private individual under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which operated on a visual flight rules flight plan. The flight originated from Fort Wayne, Indiana, at 1312, and was en route to Jeffersonville, Indiana.According to information provided by the pilot, while descending in altitude, the pilot leveled off and the engine did not respond to his throttle input. The pilot selected a diversion airfield and began troubleshooting the engine. The engine would decrease engine power with throttle movement but would not restore engine power when throttle was added. After troubleshooting the engine, the throttle would not advance past ¾ throw and the airplane was unable to maintain its altitude. Unable to make any nearby airfield, the pilot performed a forced landing to a field. The airplane's firewall was damaged during the forced landing. Examination of the airplane found that the throttle control arm was improperly fastened resulting in throttle arm slippage. It could not be determined if the throttle arm was improperly fastened during the last annual.