What Causes the RPM to Not Drop After Releasing the Throttle?
2 Answers
After releasing the throttle, the RPM may not drop due to the throttle spring being in a compressed state for a long time, resulting in reduced tension. This causes the throttle opening to increase, leading to higher fuel supply and a slower return of the RPM needle. It could also be due to faulty components or air intake leaks. If this occurs right after maintenance, the slow drop in engine RPM is not considered a fault. Engine RPM: The level of engine RPM relates to the number of work cycles per unit time or the effective power output of the engine, meaning the engine's effective power varies with RPM. Vehicle RPM Range: Different vehicle models have different idle RPM values due to varying engines. Typically, the idle RPM ranges between 500 and 850 RPM. During a cold start, the idle RPM may briefly reach 1500 to 2000 RPM, but it stabilizes within the specified range once the engine coolant temperature returns to 90 degrees.
I once encountered a situation where the RPM remained high after releasing the throttle. It was my old car, which had been running for quite some years. The throttle might have gotten stuck and didn't return to position in time. Upon inspection, it turned out that excessive carbon deposits inside were causing it to move sluggishly, and it needed to be cleaned thoroughly with a cleaning agent. A slight vacuum hose leak could also allow more air into the engine, preventing the RPM from dropping—this is common in aging cars, especially in cold weather. A faulty idle control valve is another factor; it regulates low-speed operation, and if it's sticky or the sensor signal is incorrect, the RPM can fluctuate. I tried replacing the valve myself at the time, and the issue improved significantly. In short, this kind of phenomenon should be checked as soon as possible to avoid affecting fuel efficiency and safety. Regular cleaning of the intake system can help prevent it.
