The pilot and a pilot-rated passenger were flying the home-built, experimental aircraft in the local area. The reported ceiling was 1,100 feet (broken). The aircraft was observed performing a climbing, high bank angle turn beneath the cloud deck prior to a left, descending spiral into the terrain. Several witnesses reported that there was no engine noise during the uncontrolled descent. The wreckage was located in a wooded area, about 200 yards from a highway. An examination of the wreckage indicated that the aircraft impacted the terrain in a steep, nose low attitude with little forward speed. There was evidence that the aircraft had adequate fuel for the flight. Non-volatile memory data from the engine management system indicated that the engine was at idle power at the time of ground impact. The throttle was found in the idle position, with the prop and mixture controls full forward. An examination of the engine and airframe revealed no evidence of a pre-existing malfunction or failure.