What is the effect on the engine when either engine anti-ice valve is open?

When either engine anti-ice valve is open, it allows hot air from the engine's compressor section to flow to the engine inlet to prevent ice formation. This additional airflow can influence engine performance characteristics, particularly the idle RPM. Specifically, the minimum idle RPM is increased because the engine has to work harder to maintain proper operating conditions while compensating for the loss of some of the airflow used for anti-ice purposes. This adjustment helps ensure that the engine can still operate efficiently despite the change in air dynamics caused by the open anti-ice valve.

In contrast, the other options pertain to different aspects of engine performance not directly tied to the anti-ice systems. Maximum N1 and N2 relate to the engines' speed capabilities rather than their idle settings, and the engine ignition being inhibited does not correlate with the operation of the anti-ice system.