Had the same sort of problem on a 76A, fluctuating fuel flow, N1, ITT, TQ, as one engine went up, the other went down, as you'd expect. Identified the bad engine by pulling each throttle back in turn out of governing range, having identified the bad left it just out of governing range and things settled down. Brought it home and maintenance unable to fault on a test flight with the CP. Put back on line and thirty minutes or so into the next trip one engine went to zero TQ, I knew from previous flight which was the "bad" engine and having lowered collective to contain the good engine and with hand half way to the throttle the bad engine then went from zero to max TQ in a heart beat. Turned out the drive shaft on the governor flyweights had been binding causing the hand waving of fuel flow, N1, ITT, TQ, and drive shaft ultimately sheared.