How does intake manifold vacuum relate to engine load and idle quality, and what conditions can cause abnormal vacuum readings?

How does intake manifold vacuum relate to engine load and idle quality, and what conditions can cause abnormal vacuum readings?

• A. Vacuum remains constant regardless of engine load.
• B. Vacuum is higher at heavy load and lower at light load.
• C. Abnormal vacuum readings are caused by sensor calibration alone.
• D. Abnormal vacuum readings can be caused by leaks, timing issues, misadjusted idle speed, or restricted intake.

Answer: (D)