What was found
AFTER TAKEOFF, LT PROPELLER RPM INDICATED APPROXIMATELY 20 RPM LOWER THEN THE RIGHT. LT PROP, WHEN REDUCED TO 900 RPM ALSO SHOWED 20 RPM LESS THAN THE RT. WHEN RPM WAS BROUGHT BACK TO 850 RPM THE LT ENGINE RPM ENGINE RPM DROPPED TO 700 RPM. NR 1 PEC CAUTION ILLUMINATED. NR 1 PROP RPM SURGED SEVERAL TIMES AND SETTLED AT 1060 RPM. BECAUSE OF THE ENGINE CONTROLLABILITY CONCERNS, ELECTED TO SHUTDOWN NR 1 ENGINE. AUDIBLE PROP OUT OF PHASE NOISES WERE EVIDENT PRIOR TO SHUTDOWN. RETURNED TO FIELD. LANDING UNEVENTFUL. INTERROGATED CDS AND FOUND F/C 158A/B, 236B, 260A. C/W FIM TASK, 158, 61-20-04-810-812. C/W FIM TASK, 236/237, 61-20-05-810-822. C/W FIM TASK, 260, 61-20-06-810-818. NO DEFECTS NOTED, 7/23/15.