How to Adjust a Vehicle's Idle Speed

Setting a vehicle’s idle speed correctly will have many positive effects to your vehicle. It will save you on gas, because the engine is running effectively. It will also improve acceleration and response, especially from a stopped position. If it is not set correctly, and it is too low for example, your engine could stall and die. If it’s too high, it will cause you to waste gas. An improper idle setting can also cause unnecessary wear on an engine, such as on the valves, pistons and clutch. Especially on older vehicles, you may have to occasionally adjust the idle speed in order to keep it in good running condition.

Materials

  • Flat Head Screwdriver

Step 1: Warm Up the Engine

Place the transmission in the “park” position, if your car is an automatic, or in “neutral” if your car is a manual. Start the car, and let the car idle for 5 minutes, or until the temperature gauge moves up a little.

Step 2: Locate Idle Speed Valve

Open the engine hood and find the idle speed valve. This is usually found at the end of the air intake, where it connects to the intake manifold. The valve is probably covered with a rubber or plastic cap, to protect it from being turned accidentally. Remove the cap, in order to expose an adjustment screw. This is what increases or decreases the idle of your car.

Step 3: Set the Idle Speed

Get your flat-head screwdriver and inset it into the adjustment screw. Turn the screw clockwise, in order to increase the idle, and counterclockwise to decrease it. Turn the adjustment screw accordingly, until you reach the desired idle speed of the engine. The normal idle speed for an automatic transmission ranges from 830 to 870 RPM. As for a manual transmission, the normal range would be from 680 to 720 RPM.

Step 4: Idling Testing

Once you’ve achieved the desired idle, let the car idle for a while, just to make sure that the idle does not drop while it is stationary. There are times that the idle changes soon after making the adjustment. Then, kill then engine and turn it back on after a few moments. Check again if the correct idle speed is maintained.

Step 5: Drive Testing

Get in your car and take it for a drive. Sometimes in older models, the idle speed changes when you drive your car for long distances. Drive it for a couple of miles and let it idle again. See if the idle speed has changed after you drove your car around. If it did, repeat step 3 and adjust the idle speed accordingly, depending on what change occurred. For example, if the idle speed dropped after driving it around, turn it clockwise a little bit more in order to compensate. If the idle increased after driving, lessen the idle to match it. Be sure not to set the idle speed too high or too low, in order to prevent the engine from experiencing unnecessary stress.