What effect do intake valve deposits have on engine performance?

Intake valve deposits can significantly impact engine performance, particularly in regard to volumetric efficiency and driveability. When deposits accumulate on the intake valves, they can obstruct airflow, which diminishes the engine's ability to draw in the necessary air-fuel mixture. This reduced airflow leads to a loss in volumetric efficiency, meaning the engine cannot take in as much air as it ideally should for effective combustion. This is especially detrimental during high RPM operation where optimal air intake is crucial for maintaining power output.

Additionally, these deposits can interfere with engine operation during cold starts. They may cause irregular airflow and lead to improper fuel atomization, which can result in driveability issues such as rough idling, stalling, or hesitation during acceleration. The combination of reduced volumetric efficiency and potential driveability problems during cold operation illustrates why both aspects are critical when considering the effects of intake valve deposits on engine performance. Thus, the correct answer encompasses both the reduction in efficiency at high RPMs and the potential driveability issues, making it the most comprehensive choice.