Following an avionics equipment installation, the pilot flew a local flight with a technician to check the newly installed avionics. The departure and maneuvering for a practice approach were uneventful. At glideslope intercept, the pilot brought the throttle to idle for the airplane to decelerate. After a few moments, the pilot noticed the airplane wasn’t decelerating and adjusted the propeller to help create drag to slow the airplane. About 800 ft above ground level, the pilot added throttle for a practice missed approach while the engine was running smoothly, but the engine did not respond. The pilot was unable to restore engine power and made a forced landing to a field. During the forced landing, the airplane collided with small mesquite trees and came to rest inverted resulting in substantial damage to the wings and fuselage. Postaccident examination of the airplane revealed that the throttle cable to the carburetor was found disconnected, and the castellated nut and cotter pin were not located. The recent avionics installation required the temporary removal of the engine throttle cable. Based on available evidence, it is likely that the mechanic did not properly reinstall the cotter pin resulting in the separation of the cable and a loss of engine throttle cable control.