As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE TROUBLESHOOTING ENGINE FOR SURGING PROBLEM. AIRFLOW MODULATOR WAS CHANGED. FILTER ELBOW HAS TO BE TRANSFERED TO NEW MODULATOR. FOUND FILTER SCREEN TO BE LOOSE INSIDE ELBOW AT THIS TIME. BROKEN FILTER HAD NO EFFECT ON THIS SURGING PROBLEM. MUST INSPECT FILTER ELBOW WHEN CHANGING AIRFLOW MODULATOR.