What was found
FLT#2033, BOS-IAH. (AIRCRAFT PERFORMED AN AIR TURN BACK) ' AT FL340 DURING CRUISE, RECEIVED L ENGINE FAULT ADVISORY MSG ON EICAS WITH '79 L ENGINE FAULT OIL DEBRIS ABOVE LIMIT INFO MESSAGE NO ECL ABOUT 30-45 SECONDS LATER RECEIVED AMBER ENGINE VIBRATION EICAS MSG NO VIBE LEVEL NOTED MESSAGE CLEARED AFTER 5-10 SECONDS ABOUT 30 MIN LATER L ENGINE FAULT AND INFO MSG CLEARED ABOUT 35 MINUTES BEFORE LANDING PRIOR TO TOP OF DESCENT ALL MESSAGES RETURNED IN SAME SEQUENCE AS ABOVE PRIMARY DIFFERENCE WAS ENGINE VIBRATION SHOWED VALUE AS HIGH AS 8.0 FOR BRIEF MOMENTS THEN CLEARED BEFORE ECL WAS COMPLETED PRINTED REPORT WAS GENERATED.' (SUPPLEMENTAL INFORMATION TO FOLLOW)