First time running up this season on with a Yanmar 3GM30FV. My idle speed will not go below 1600 rpm. I had some corrosion develop around the the governor linkage which stuck my throttle, however, i cleared that up with some lubricating oil and elbow grease. The engine runs fine up to 3600 rpm as specified. I just replaced the 180º mixing elbow on the exhaust due to a blockage in the passage for cooling water. One of my thoughts is the idle was progressively adjusted as constriction increased in the old elbow, increasing exhaust backpressure. I'm hung up on the fact that a backpressure problem would affect the top end of the rpms, not idling speed. Any thoughts? I bought the boat last summer and noticed the cooling water problem develop after a few months. I don't want to haphazardly adjust the idle stop, considering I've never had a diesel that needed idle adjustment as often as a gasser carb retune.