Normally, I might have panicked, but with my experienced copilot at my side, I stayed calm. We talked through our options and decisions along as I continued to fly the plane. I began a series of small adjustments to the throttle and mixture to see how the engine responded. We quickly discovered these changes only made matters worse, so we left the settings as is. My buddy reminded me to stay high-altitude is our friend-and we looked for landing spots in case things deteriorated.