As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE VACUUM TRANSDUCER WAS INCORRECTLY INDICATING LOW VACUUM AND DIDN'T ENTER THE DESIRED OPERATING RANGE UNTIL 2000RPM (THE AMM CALLS FOR THE VACUUM TO REACH DESIRED RANGE AT 1200 RPM). REMOVED AND REPLACED THE VACUUM TRANSDUCER WITH NEW P/N P-165-5786 (8130-3) IAW CESSNA/TEXTRON 172 SERIES (1996 & ON) AMM REV. 23 CHAP. 37-10-00. FUNCTIONAL TEST AFTER THIS REPLACEMENT WAS GOOD.