As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AUTOPILOT EVALUATION REQUESTED PER M1A 028521-64/2. AUTOPILOT EVALUATION WAS UNSATISFACTORY. HEADING BUG DID NOT OVERSHOOT AND THERE WASN'T EXCESSIVE BANK BUT THERE WAS RESISTANT VIBRATION IN THE ELEVATOR WITH AUTOPILOT ENGAGED. REPLACED THE AUTOPILOT PITCH COMPUTER IAW DC9 AMM 22-13-01.