After mazda 6 overhauled the engine, the oil light came on.

Maybe it's because the throttle is dirty and stuck. When the engine is in gear, the speed is low due to the load. When you turn off the throttle, the load disappears and the throttle cannot be completely turned off, resulting in a gradual increase in speed. I suggest you go to the 4S shop to check and clean the throttle valve and make initialization settings.