Why does the engine speed remain high during cold starts in summer?

[LeNaomi]

There are mainly the following reasons for high engine speed during cold starts in summer: 1. Generally, the idle speed during cold starts tends to be higher because it varies with ambient temperature. It's normal for cold start speed to remain within 2000 RPM. 2. During cold starts, the engine speed is automatically adjusted by the ECU based on signals received from the coolant temperature sensor and oxygen sensor. When the vehicle's computer detects changes in coolant temperature or variations in the oxygen sensor's feedback voltage, it continuously corrects the fuel injector's fuel delivery quantity. Therefore, before the engine reaches optimal operating temperature, the ECU's continuous fuel adjustment causes corresponding fluctuations in engine speed.

[StLawson]

High RPM during cold starts in summer is something I've encountered many times over my 20 years of driving. Mainly because summer heat makes the air thinner, and the engine's computer automatically injects more fuel to maintain the air-fuel mixture ratio, which raises the RPM. Excessive carbon buildup in the throttle body can also restrict airflow, leading to high RPM. I regularly clean the throttle body to prevent this issue. Additionally, faulty sensors like the intake temperature or oxygen sensors might mislead the computer, so they should be checked. High RPM not only increases noise but also fuel consumption. I recommend parking in the shade during hot weather and waiting for about a minute after starting until the RPM drops before driving to ensure safety. Don't underestimate it—it can damage the engine.

[Cavalcanti]

I was startled by the sudden high RPM during cold starts in the first summer after buying my car. After researching, I learned that in hot summer weather, the lower air density causes the ECU to compensate by injecting more fuel, resulting in higher RPM. Alternatively, it could be due to the AC compressor engaging and consuming engine power. I also tried pre-warming the engine for a few minutes before driving when the car was already hot, which seemed to help significantly. At the repair shop, they found the throttle body was slightly dirty and cleaned it. After checking that the sensor connectors weren't loose, the issue disappeared. This phenomenon is generally normal, but long-term attention should be paid to potential increased fuel consumption affecting engine lifespan. With proper maintenance, it should be fine.

[McNadia]

High cold start RPM is more common in summer, possibly due to inaccurate intake temperature sensor signals misleading the ECU to supply more fuel, or poor fuel quality with strong volatility causing incomplete combustion and elevated RPM. Excessive carbon deposits blocking the throttle body and restricting airflow can also cause this. I used diagnostic tools to troubleshoot, cleaned the intake tract, and switched to better engine oil to resolve it. Don't ignore high RPM increasing wear - parking in shade during summer and starting smoothly before driving is safer.