Why does the engine RPM drop slowly when releasing the throttle?
3 Answers
Reasons for slow RPM drop when releasing the throttle are as follows: 1. This may be caused by an over-rich air-fuel mixture in the engine, which can result from various factors; 2. It might be due to malfunctioning sensors. Proper engine operation relies on numerous sensors and electronic components - if certain sensors fail, it may cause abnormal engine performance. Below is relevant information about engine sensors: 1. Sensors around the engine include oxygen sensors, mass airflow sensors, intake air temperature sensors, camshaft position sensors, coolant temperature sensors, etc. 2. If any sensor malfunctions, it may cause the engine to exhibit an over-rich mixture condition, resulting in minimal RPM reduction when releasing the throttle pedal.
I often encounter this situation where the engine RPM drops very slowly after releasing the throttle, mainly caused by throttle system issues. For example, if the throttle cable gets stuck, lack of lubrication over time can make it stiff and prevent the throttle from closing properly; in fuel-injected vehicles, carbon buildup on the throttle body or inaccurate signals from the throttle position sensor can also cause delayed RPM drop. Sometimes minor air leaks in the intake manifold or unstable vacuum systems can lead to similar problems, or there might be an engine control unit malfunction requiring a software update. This affects driving smoothness, especially when decelerating isn't smooth during mountain road turns. I recommend first checking if the throttle pedal returns smoothly on your own. If not, then take it to a repair shop for professional diagnosis to prevent minor issues from turning into major repairs. Regular throttle body cleaning and component lubrication can effectively prevent such problems.
My car also had the issue of sticky throttle response when releasing the pedal, mostly caused by minor problems accumulated from daily use. For example, frequent driving can lead to dust buildup on the throttle cable, making it stick and causing a delayed response when closing; or a dirty throttle body with thick carbon deposits can cause sensors to misread, leading the ECU to misinterpret idle conditions. Try lightly pressing the throttle a few times to check the return force, or let the car idle for a few minutes after startup for automatic calibration. If the RPM remains high and doesn’t drop, it might also be related to a clogged air filter or uneven fuel supply, which can increase fuel consumption and waste money. If you want to DIY, ask a friend to help lubricate the cable or simply clean the intake tract—often that solves the problem. If it still persists, getting a checkup at a 4S shop isn’t a hassle, so don’t delay and risk bigger issues.
