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The impact of the TAC (Throttle Actuator Control) system during engine cranking primarily focuses on how it manages engine airflow and fuel delivery, ultimately influencing combustion efficiency. When the TAC system is properly functioning during cranking, it can help ensure that the engine receives the optimal air-fuel mixture, which is critical for effective combustion.

During this phase, the efficient mixing of air and fuel leads to a more complete combustion process, somewhat reducing the formation of nitrogen oxides (NOx), which are typically produced in higher quantities under conditions of incomplete combustion and high combustion temperatures. As a result, the TAC system's ability to regulate airflow and optimize fuel utilization directly correlates with a decrease in NOx emissions during initial engine cranking.

In contrast, options suggesting an increase, no effect, or fluctuations in NOx levels do not accurately reflect the operational goals of the TAC system during this critical starting phase. The system's design typically aims to enhance combustion efficiency, which naturally leads to reduced NOx emissions.