As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE VACUUM REGULATOR VALVE WAS COMPLETELY INOPERABLE. VACUUM SYSTEM INDICATION WAS DIRECTLY PROPORTIONAL TO THE ENGINE RMP. REMOVED VACUUM REGULATOR VALVE PN: AA2H3-2, SN 2-27216 AND INSTALLED NEW PN: AA2H3-2, SN: 2-0HJH04 (8130-3) IAW CESSNA/TEXTRON 172 SERIES (1996 & ON) AMM REV. 23 CHAP. 37-10-00.