Just purchased a 1998 ranger with a mercury 115 hp<br />outboard. When "on plane" I take my hand off the throttle the boat slows down as though the throttle is slipping. I put my hand back on throttle and give a little gas it picks up and runs fine. I wonder it this is some sort of safety feature or am I having a problem with the throttle. control. Any thoughts as to what is causing this?