The idle speed is controlled by the throttle. Most cars have the optimum idle speed set in the factory. But over time and with wear, the speed changes. Checking the idle speed is an important part of car maintenance. The proper idle speed will increase gas mileage and reduce undue wear on the engine. Since the car must be in "Drive," the job requires two people for an Accord with an automatic transmission. One person to adjust the idle, and the other to sit in the car with their foot on the brake.
Start the car, and allow the motor to run for several minutes. Engage the parking brake.
Open the bonnet of the car. Under the bonnet, there will be a decal with the factory-recommended idle speed.
Instruct the driver to put her foot on the brake, and put the transmission in "Drive." If the car has a manual transmission, you can leave it in neutral.
Compare the idle speed shown on the Accord's tachometer to the recommended speed.
Locate the idle-adjustment screw. In the Accord, it is on the left-hand side of the throttle assembly. The entire assembly is located toward the back of the engine, near the firewall. The screw will have a small spring separating it from the throttle assembly.
Use a long screwdriver to turn the screw clockwise to open the throttle and speed up the idle. If the idle speed is already too high, turn the screw counterclockwise to close the throttle. When the optimal speed is reached, instruct the driver to rev the engine a few times to ensure that the idle will remain steady.
Instruct the driver to put the car in "Park" and turn off the car. Close the bonnet.
If you suspect your tachometer is faulty, you can use an external tachometer or a timing light with a tachometer function.
Never leave an unattended car in gear.