By "fluctuate" what do you mean?
Mine sometimes drop to zero and come back. They never go above the actual fuel flow, however.
Do you have any other ways to read the fuel flow? In my airplane, the Garmin units are connected to the fuel flow, and I can read it on them (in my case, they never wobble). Another thing to check is the behavior of the fuel counter. It should reflect the reading of the fuel flow gauges, unless the gauge itself or the associated wiring is the issue.
On my airplane, it usually does it after the airplane hasn't flown for a few weeks. After an hour or two, it works normally from then on.