2009 Yamaha 60 hp 4 stroke surges at low docking speeds

by Brian
(North Bay, ON, Canada)

We just purchased a Sunchaser 820 Pontoon Boat with a Yamaha 60 HP 4 stroke. 6 years old but very little use, under 10 hours. Engine starts and runs beautifully except that on 3 occasions in the last week when I was doing very low speed docking and I slightly adjusted the throttle the engine would surge as RPMs increased and Of course made a noise as I tried to get in back in Neutral. This doesn't happen every time I dock. Yesterday the RPMs were going crazy and I had to shut engine off. I waited 20-30 seconds and it started and no further problem. I have read of other posts where anti-siphon valve in fuel tank was the culprit with crud gumming it up. Others suggest Throttle Speed Sensor could be faulty. My day or so Google research indicates it may be the Idle Air Control Valve needing cleaning or replacement. We dock at a small campground and Marina and the owner looks after many types of engines but I doubt he has laptop software to analyse fault codes so I am trying to narrow down possibilities before I leave it with him. I may have to trailer it into North Bay, ON to see the Yamaha Tech but hopefully we can deal with it at the marina. Dose of Ring Tune or SeaFoam probably wouldn't hurt. Engine runs beautifully except for these occasional surges at very low speed when docking. It concerns me especially in a high wind situation and of course my wife is scared to operate it after 35 years running our 90 hp Mariner without any issues. Hopefully the excellent Forum Members can assist.