Why does the engine speed not drop after releasing the accelerator pedal?
3 Answers
If the engine speed does not drop after releasing the accelerator pedal, it may be 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 slower return of the RPM needle. It could also be caused by faulty components or air leaks in the intake system. If this happens right after maintenance, the slow drop in engine speed is not considered a malfunction. The engine speed determines the number of power strokes per unit time or the effective power output of the engine. The effective power varies with different speeds, so when specifying engine power, the corresponding speed must also be indicated. The rated power and rated speed specified on the engine nameplate refer to the effective power and corresponding speed under standard conditions.
I've encountered a similar issue when driving a manual transmission car—the tachometer needle stays stuck at 3000 RPM after releasing the throttle. Common causes could be a stuck throttle cable or excessive carbon buildup in the throttle body. Nowadays, many cars have electronic throttles, and a faulty throttle position sensor can also cause this. Last time, my car had a dirty throttle body—the throttle plate could open when pressing the accelerator, but the return spring was obstructed. Cleaning the throttle body finally fixed it. For older cars, it's also important to check if the idle air control valve is stuck, as these are key components affecting RPM drop. A weak battery causing ECU malfunctions could also lead to this issue—try simply restarting the engine to see if it resolves.
This is a common issue seen in repair shops, and quite a few vehicles suffer from it. The main areas to check are: air intake system leaks, throttle valve carbon buildup, and electronic throttle control malfunctions. Last time, when working on a Nissan, we found that a crack in the intake pipe caused the ECU to misjudge the air intake volume, preventing the idle speed from dropping. Another case involved a Volkswagen where the crankcase ventilation valve leaked oil and clogged the throttle—cleaning it fixed the problem. For turbocharged vehicles, pay attention to whether the vacuum hose is cracked, as it can affect the intake pressure sensor data. You can start by checking for any hissing sounds in the engine bay and observing if the RPM changes abnormally when pulling out the oil dipstick. These are quick diagnostic tips.
