The ECM uses the signal from the CPS for fuel injection timing could be loose and as engine heats up the sensor moves, a bad connection or just a bad sensor! if you have a ohm meter you can check sensor Unplug the sensor at its connection and it should have about 580 ohms resistance in the wires from the sensor. But I would just let Polaris dealer take care of it! Hoping the service tech at your dealer is one of the good ones! keep us informed!