The pilot stated that as he started his descent and reduced engine power, he felt a "bump" in the throttle. The engine's rpm dropped and the engine lost power. The pilot established his glide and elected to conduct a forced landing to a nearby airport. Additionally, the pilot reported that moving the throttle had no effect on engine power, however the engine would oscillate between idle and full power. The airplane was substantially damaged during the forced landing. A Federal Aviation Administration (FAA) inspector who traveled to the site reported that the nut securing the throttle linkage to the carburetor's control lever was missing and the throttle linkage was found disconnected. A review of the manufacturer's maintenance manual revealed the approved parts included a bolt with a fiber-locking nut.