The car runs perfectly, but sometimes, seemingly completely randomly, the tachometer will start reading 1000 less than it should. so it idles at -100~ and when I step on it it only goes up to 4 if I am at 5. if I turn it off and back on it doesn't change but it just goes back to normal a few minutes later. It happened 3 times. I can drive based on sound, but what that be stepper motor or something else?