My needle wiggles and jiggles. At WOT it goes past 240,reduce speed slightly and it rapidly drops to 190. At 35mph or 4600rpms it reads 190. In no wake it reads about 180 after about five minutes. When I give it the gas it imediately goes to approx. 230 then comes down to about 190. Confused? Any ideas? Its a 1997 135 Mer. I/O
