Engine throttle opening and closing sequence

If you don't count the coincidence angle!

When cylinder 3 is at compression top dead center, the intake valve and exhaust valve are closed; Cylinder 4 is a power stroke, so the intake valve and exhaust valve are closed; Cylinder 2 is the exhaust stroke, the intake valve is closed and the exhaust valve is opened; 1 cylinder is the intake stroke, then the intake valve opens and the exhaust valve closes!