My 1023E which I purchased used with about 75 hrs on it in March seemed to me to be idling too fast. Around 1500 - 1600 rpm. So I pulled off the cowling and starting adjusting the idle speed set screw. As I started slowing it down the engine vibration got worse and worse, to the point where the whole tractor was shaking and I thought the thing was going to come loose from the engine mounts. So I put it back up to about 1300. Less than what it was but still a lot higher than I thought it should be. At that point the engine vibration is minimal. As you increase rpm to working speeds it runs smoother and smoother. The diesel in my Jeep Grand Cherokee idles at about 600 - 700 rpm. Are these Yanmar engines simply not supposed to idle that slow of is something wrong with this particular engine?