Apparatus and method for engine cylinder intake air quantity calculation

A cylinder intake air mass quantity for an engine is calculated in accordance with the cylinder intake air volume quantity, the manifold air mass quantity and a manifold volume. The cylinder intake air volume quantity is calculated in accordance with a cylinder volume at an intake valve closing timing. The manifold air mass quantity is calculated from a balance between an intake manifold inflow air mass quantity and an intake manifold outflow air mass quantity. The manifold inflow air mass quantityQa. DELTA t is reset to a minimum setting value when an engine stop state with no intake air induction is detected.