yeah probably the speed sensor... if you dont know where it is, its located right behind the engine near the rear motor mount. it has a red or orange cap i think. you might have to remove the battery to get to it. it gets worked loose because of all the motor shaking. also, the clip on it can break easily, making it very easy to fall off.
the clip on mine broke and i had to silicone it down with RTV. let us know what happens.
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