Misfire due to carbon build up on exhaust valves on Jeep Grand Cherokee

4.0L 6 Cylinder Due to misfires, you may experience a loss of power when accelerating between 50 and 70 MPH (most noticeable below 32° F). This is commonly caused by carbon buildup on the valve stems, as a result the exhaust valves may close too late. All of the exhaust valves should be inspected and if necessary the engine should be decarbonized.