How to Lower Excessive Idle Speed?

[KathrynAnn]

Ensure there is a gap after fully releasing the throttle grip, install the air filter properly, start the engine and warm it up first, then open the choke. Screw the air adjustment screw all the way in, then reverse it by one turn. Next, adjust the throttle screw to ensure the throttle grip is fully released. Lower the idle speed to reduce the engine RPM as much as possible. Then increase the idle speed, also adjusting the air adjustment screw, to make the engine RPM as high as possible. Repeat these steps several times until you find a satisfactory idle speed.

[KadenLee]

I've driven a taxi for over 20 years, and high idle speed is a common issue. First, check if the throttle cable is stuck or if there's too much carbon buildup in the throttle body—these are the usual culprits for high idle. For older mechanical throttle bodies, there's an idle adjustment screw under the hood that you can manually turn, but make sure to adjust it when the engine is warm. After adjusting, keep an eye on the tachometer to ensure it doesn't drop below 600 RPM. For modern cars, don't try to fix it yourself—most likely, it's an electronic throttle that needs computer calibration, or issues like an intake leak or a faulty coolant temperature sensor. Once, after adjusting, I noticed fuel consumption skyrocketing, only to find a cracked vacuum hose causing a leak. Adjusting idle speed isn't hard, but the key is identifying the root cause first—otherwise, you might end up with more problems.

[BlakelyLee]

Last month, my car's idle speed suddenly shot up to 1500 RPM, and it took me quite a while to figure out the issue. First, check the throttle body—when I opened it up, it was completely covered in black sludge. After cleaning it thoroughly with carburetor cleaner and reinstalling it, the idle speed immediately dropped by 300 RPM. If it's a cable-operated throttle, look for the small screw with a spring near the throttle body and turn it counterclockwise by a quarter turn to lower the idle speed. However, you'll need to adjust it gradually while monitoring the tachometer, as turning it too much can cause the engine to stall. Fuel-injected cars are more troublesome—it could be a stuck idle control valve or a faulty mass airflow sensor. My neighbor, for instance, followed a TikTok tutorial and messed with the ECU, resulting in unstable idle speed and an 800-yuan repair bill. In reality, cleaning the idle control valve can solve most issues. If that doesn’t work, you’ll need to use a diagnostic tool to read the trouble codes.

[StJulian]

After ten years of repairing cars, I've found that high idle speed is often a minor issue leading to major problems. First, pop the hood and listen for any hissing sounds indicating air leaks—cracks in the intake pipe can allow excess air into the engine, causing idle speed to surge. Next, check the throttle position sensor; if it's dirty, it might falsely report the throttle opening. For fuel-injected cars, avoid casually adjusting the idle speed screw, as the ECU has a self-learning function that could get disrupted. Last time, a customer's car idled at 1200 RPM, and replacing the oxygen sensor fixed it. Cable throttles are simpler—after adjusting the screw, rev the engine a couple of times to stabilize the idle. If all else fails, inspect the spark plug gap and ignition timing; a gap that's too wide can affect idle speed. These tasks might seem straightforward, but without experience, it's safer to take the car to a repair shop.

[CatherineFitz]

When my old Jetta had high idle speed, the mechanic taught me this trick: After warming up the engine, unplug the throttle position sensor connector. If the idle speed drops, it means the sensor is faulty. For mechanical throttle bodies, locate the adjustment screw with a lock nut on the base, loosen the nut, and turn the adjustment screw—clockwise to increase and counterclockwise to decrease idle speed. Adjust in 1/4-turn increments, waiting 10 seconds each time to observe RPM changes. Nowadays, new cars use electronic throttle bodies, requiring a diagnostic tool to perform throttle adaptation in the engine control system. Once, after cleaning the throttle body without adaptation, my idle speed stayed stuck at 1500 RPM. Also, check vacuum hoses and the PCV valve—aged rubber tubes with air leaks can cause erratic idle fluctuations.

[DiDylan]

I've had firsthand experience with erratic idle speeds, and the key is not to rush into adjusting screws. First, clean the throttle body and idle air control valve—carbon buildup blocking the intake passages is the most common culprit. For fuel-injected vehicles, try disconnecting the negative battery terminal for ten minutes to reset the ECU. For cable-operated throttles, check if the throttle pedal return spring is sticking, and spray WD-40 on the cable pivot points. Last time, cleaning my EGR valve made an immediate difference—a stuck valve disrupts exhaust gas recirculation. Here's a lesser-known cause: a faulty coolant temperature sensor can trick the ECU into misjudging engine warm-up status. If all else fails, inspect the fuel pressure regulator—excessive fuel pressure can also elevate idle speed.