As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRPLANE HAS PITCH OSCILLATION (PORPOISES) WITH ANY AUTOPILOT IN COMMAND AND (V-S, ALT HOLD, VNAV, FLCH) MODE SELECTED. CREW COMMENTS: CTR AP PORPOISES 300FPM +-- 20FTL AP 400 FPM +-- 20FTRT AP OK. PERFORM CAT3 FUNCTION TEST. ALL PASSED BY CMC AND NO MSG FOUND PER MM. NEED CREW KEEP MONITOR AND RECOMMEND.