Why does the oil light come on when the car come to a stop

Low oil pressure.

Hello, The low oil pressure light coming on when the engine is idling says there is likely heavy oil sludge or just a failing oil pump. Oil pressure is lowest when idling, and that is because the oil pump spins at the same speed as the engine. When the engine speed picks up, oil pressure increases. That being said, it is going to cost much less to have the issue diagnosed than to replace the engine.