Idle speed behavior after cold start — statement validation An engine’s idle speed rises slightly just after a cold start, then drops as the engine warms up and stabilises at the normal specification. Is this statement correct?

Introduction / Context:
Modern engines use fast-idle strategies to improve driveability, reduce emissions, and speed warm-up. Understanding post-start idle control helps diagnose idle complaints and verify proper sensor operation.

Given Data / Assumptions:

• Closed-loop fuel-injected engine with idle air control (IAC) or electronic throttle control (ETC).
• Cold start conditions and normal warm-up.

Concept / Approach:
At cold start, friction is higher and fuel atomisation is poorer. The ECU commands a higher idle speed and richer mixture to stabilise combustion and quickly bring catalysts to light-off temperature. As coolant and intake temperatures rise, the ECU progressively reduces the commanded idle to the standard setpoint.

Step-by-Step Solution:
Cold start detected by coolant and intake temperature sensors.ECU increases idle airflow (IAC/ETC) and enriches fueling.As engine warms, airflow and fueling are tapered back → idle returns to specification.

Verification / Alternative check:
Scan-tool live data shows commanded idle higher when coolant is cold; after a few minutes, RPM decreases to the nominal base idle.

Why Other Options Are Wrong:

• False: contradicts standard calibration strategies used to meet emissions and driveability requirements.

Common Pitfalls:
Assuming a stuck high idle when engine is simply cold; diagnose only after warm-up. Vacuum leaks can also cause high warm idle and should be ruled out.

Final Answer:
True