Which PID in this data log, taken during idle, shows a vehicle concern?

Which PID in this data log, taken during idle, shows a vehicle concern?

• A. RPM
• B. TPS
• C. IAT
• D. MAP

Answer: (C)

The key idea is how the engine’s fueling is tuned during idle. The intake air temperature reading is used by the engine control unit to adjust air density and therefore how much fuel to inject. If this sensor reports an unexpected temperature—unusually high or low compared with the ambient air—the ECU will miscalculate fueling, often causing rough idle, stalling, or inconsistent idle quality. That makes the intake air temperature reading a direct indicator of a concern in an idle data log, because it points to a sensor issue or air-interaction problem that can drive idle problems. RPM, throttle position, and manifold pressure can all signal issues, but they’re less diagnostic of a sensor fault during idle on their own. RPM should be steady, TPS should be near closed, and MAP reflects vacuum, but an out-of-range intake air temperature most clearly explains abnormal idle behavior due to incorrect fueling.

The key idea is how the engine’s fueling is tuned during idle. The intake air temperature reading is used by the engine control unit to adjust air density and therefore how much fuel to inject. If this sensor reports an unexpected temperature—unusually high or low compared with the ambient air—the ECU will miscalculate fueling, often causing rough idle, stalling, or inconsistent idle quality. That makes the intake air temperature reading a direct indicator of a concern in an idle data log, because it points to a sensor issue or air-interaction problem that can drive idle problems.

RPM, throttle position, and manifold pressure can all signal issues, but they’re less diagnostic of a sensor fault during idle on their own. RPM should be steady, TPS should be near closed, and MAP reflects vacuum, but an out-of-range intake air temperature most clearly explains abnormal idle behavior due to incorrect fueling.