Why does the engine speed not drop after releasing the accelerator pedal?

[AngelinaMarie]

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.

[DiAlivia]

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.

[LeBella]

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.

[GriffinMarie]

This issue involves engine control logic. When the throttle is released, the ECU reduces fuel injection. However, if additional air enters the combustion chamber, such as when the throttle is stuck in the open position or there's an intake pipe leak, the ECU will actually increase fuel supply to maintain operation. Based on my experience, the focus should be on checking the electronic throttle and the charcoal canister solenoid valve. If the solenoid valve is stuck open, it will continuously introduce fuel vapor. Additionally, for electronic throttle vehicles like the Magotan, a faulty APP sensor can persistently provide incorrect throttle position signals. Using a diagnostic tool to read the data stream can clearly show the throttle opening rate variation, which is usually the fastest way to pinpoint the fault.

[StLeila]

Encountered several cases where minor issues were the culprits. For instance, the floor mat got stuck under the accelerator pedal, and upon disassembly, it was indeed the case—the driver hadn't even noticed. More commonly, it's the clutch switch failure, especially in manual transmission vehicles. When the switch is damaged, the ECU always thinks the clutch is engaged, keeping the engine at high RPMs ready for takeoff. For automatic transmissions, it's essential to check if the brake light switch has failed, as this can affect the transmission's shifting logic. Older models should be particularly wary of idle control valve failure. I recall a Buick Regal that ran worse after cleaning the throttle body, and only replacing the idle valve fixed the issue. It's advisable to start with the most basic checks: confirm the floor mat's position and listen for any air leaks in the engine bay.

[Athena]

My female neighbor asked about this issue just last week. Actually, she encountered the simplest scenario: the throttle body had just been cleaned but no computer matching was performed. Nowadays, electronic throttle bodies require a reset learning process, and dealerships use diagnostic tools for matching. You can also do it yourself: disconnect the negative battery terminal for ten minutes to reset the ECU. If the air filter was recently replaced and not installed properly, causing air leaks, the RPM will also be abnormal. Daily use requires attention to tightening the fuel tank cap after refueling, as issues with the fuel vapor recovery system can also trigger abnormal RPM. A key reminder is not to overlook small parts—my Sagitar once had a broken return spring on the accelerator pedal, which cost only about a hundred yuan to replace.