What was found
AIRCRAFT HAD A LOUD BANG AND MOVED TO THE LEFT. PASSENGERS HEARD AND FELT THE NOISE. AFTER 10 MINUTES ALL LEFT ENGINE PARAMETERS SURGED BACK AND FORTH. IAW AMM 79-21-05, LT ENGINE OIL SYSTEM MAGNETIC CHIP DETECTOR CHECK AND SERVICE. ACCOMPLISHED VSV ACTUATION HARDWARE FOR DAMAGE AND EXAMINED THE VBV ACTUATION HARDWARE FOR DAMAGE IAW 75-31-03-216-002-H00 AND 75-32-01-206-005-H00. ACCOMPLISHED POWER ASSURANCE RUN AND VERIFY LEFT ENGINE PARAMERTERS ARE NORMAL. THE AIRCRAFT WAS GROUNDED.