stx 15f, someone please give me advice before i pick up from dealer tomorrow.
 

alright so ill break a long story to short. i have a 2008 kawasaki stx 15f for 2 summers already and never has an issue until last week. i took it out for a ride with me and my friend stopped at the beach and when i pushed the jet ski back in to the water and started it right off the first touch of acceleration i felt something weird with the ski. it felt harsh and engine vibrations as if something was stuck in the impeller. i tried reversing it out and it was still there. i took it back to the marina a mile away and it was still happening not letting the ski reach to its max. i let the ski run on 10mph and it all of a sudden opened up to normal. 2 days later i take it for a ride full speed and i start feeling a kick of loss power and then the f1 started to blink. i took it to the dealer and they are saying that there is nothing wrong with the ski and its riding like a baby in their pool. what should i do or look at?
ps facing the front with the seat off there is a sensor by the engine which is the fuel injector sensor( small chip) it can easily be pulled out, could that be the cause?