How to Adjust the Idle on Cars

by Contributing Writer

Adjust the idle of your car if the engine runs too fast or too slowly, causing it to sputter and die.

Under The Hood:

 How to Adjust the Idle on a Honda 50R Bike

Start the motor and let it run for between 2 and 5 minutes to allow the motor to warm to its operating temperature.

Locate the Phillips idle adjustment screw on the right side of the carburetor.

Turn the idle adjustment screw clockwise with a Phillips screwdriver to increase the engine's idle speed. Turn the screw counterclockwise to lower the idle speed.

Adjust the engine idle speed so that the motor is running smoothly without chugging or racing. Stop the motor.

Items you will need

  • Phillips screwdriver

 How to Adjust the Idle on a Polaris RZR

Set the brake and shift the transmission into neutral. Start the engine and let it warm up at idle for about five minutes. Turn the engine off.

Look through the right-side front wheel well and locate the throttle cable adjuster. Squeeze the small end of the protective boot and carefully pull back the boot to expose the adjuster. Using a pair of open-end wrenches, loosen the locknut, then collapse the adjuster to slacken the throttle cable.

Locate the carburetor at the end of the air-cleaner discharge pipe, then locate the idle speed adjuster screw on the side of the carburetor, near the slide tower. Start the engine. Using a No. 2 Phillips screwdriver, adjust the screw in or out to raise or lower the rpm as needed until the rpm is acceptable. There is no set specification for idle on the RZR 170. Set the idle speed high enough that the engine does not stall and low enough that it will shift smoothly. Turn the engine off.

Extend the throttle cable adjuster, while monitoring the freeplay at the throttle pedal. Adjust the cable until you have 1/16 to 1/8 inch of freeplay at the pedal before the cable begins to actuate the slide in the carburetor.

Using a pair of open-end wrenches, tighten the adjuster locknut. Wipe a light coat of grease in the boot, and slide it over the adjuster. Test drive the RZR.

Items you will need

  • Open-end wrench set

  • No. 2 Phillips screwdriver

  • Grease

 How to Adjust Idle on a Jeep Cherokee

Preparations

Connect the tachometer to the vehicle following the tachometer manufacturer's instructions. Exact attachment depends on your tachometer's make and model. Be certain any wires are clear of the fan and other moving engine parts.

Set the parking brake. Shift the automatic transmission to "park" or manual transmission to "neutral."

Start the engine and allow it to run until it reaches normal operating temperature (upper coolant hose will be hot). Shut off the engine, as well as the air conditioner.

Disconnect the vacuum line from the carburetor sol-vac actuator (four-cylinder models) or the exhaust gas recirculation valve (V6 models). Plug the disconnected vacuum lines.

Idle Speed Check and Adjustment.

Start the engine. Check the idle speed with the tachometer. For manual transmissions, the shifter should be in "neutral." For automatic transmissions, the shifter should be in "drive." Have an assistant shift to "drive" while holding the brake pedal down.

Compare the idle speed to the specifications on the vehicle emission control information sticker, which is in the engine compartment. Normal idle speed is 700 to 750 rpm. Use this value if the sticker is missing or damaged. If the idle speed is correct, you are finished. Shut off the engine, disconnect the tachometer and re-connect the vacuum lines.

Adjust the idle speed by turning the idle speed adjusting screw on the carburetor (V6 models) or by turning the 1/4-inch nut on the sol-vac vacuum actuator (four-cylinder models). Turn clockwise to increase idle speed, counterclockwise to decrease idle speed.

Shut off the engine, disconnect the tachometer and re-connect the vacuum lines.

Items you will need

  • Small (1/4-inch or adjustable) wrench or pliers

  • Flat-head screwdriver

  • Tachometer

 How to Adjust the Idle in a 1998 Jeep Cherokee

Open the hood of your 1998 Jeep Cherokee. Find the throttle body straight back from the A/C compressor, to the left of the fuel injector and to the immediate right of the air intake temperature sensor on the engine block. The idle air control valve is a black plastic part approximately two inches long that is attached to the throttle body.

Grab the oval electrical connector that is connected to the idle air control valve and pull it away from the valve to disconnect it.

Use a Phillips head screwdriver to remove the two screws that hold the valve in place.

Use a rubber mallet to tap the valve body loose from its position.

Thoroughly clean the idle valve with a shop rag and an aerosol carburetor cleaner. There will be a build up of oil and carbon on the valve that may be causing your normal idle to falter. Use only aerosol carburetor cleaner on the valve parts -- not on the sensors or anything else around the engine area.

Put the idle valve back in place, start the Cherokee and see if this has rectified the problem. If not, take the valve off again and proceed to the next step.

Purchase a new idle air control valve from an auto parts store or online distributor. Make sure to tell them the year and model of your Jeep to get the proper part.

Position the new idle control valve in place and secure it with the two screws you removed earlier. Connect the oval electrical connector by pushing it into place where you removed it in Step 2. If replacing the idle valve with this new one has not fixed the problem, consult a mechanic for further inspection and for advice on possible problems.

Items you will need

  • Phillips head screwdriver

  • Shop rag

  • Rubber mallet

  • Aerosol carburetor cleaner

  • Replacement idle air control valve, if needed

 How to Adjust the Idle of a 1991 Chevy

Put the wheel chocks around the front wheels of the Chevrolet and set the parking brake. Pop the hood and take off the air cleaner on the engine by taking off the factory wingnut with your hands and setting the air cleaner away from the engine bay.

Have your assistant start the engine. Let the engine get to normal operating temperature. Locate the throttle cable linkage, which is on the driver's side of the carburetor, just below the bowl where the air cleaner mounts. Locate the adjusting screw, which is just above the throttle linkage. Locate the vehicle specifications sticker, which is on the underside of the hood, and lists the factory idle speed setting.

Tighten down the adjusting screw on the throttle cable linkage with the flathead screwdriver to raise the idle speed, and loosen the screw to lower the idle speed. Have your assistant call out the RPMs listed on the tachometer in the dashboard as you adjust until you reach the idle speed that you prefer or that Chevrolet recommends on the underhood sticker.

Items you will need

  • Flathead screwdriver

  • Flashlight

  • Assistant

  • Wheel chocks

 How to Adjust the Idle on a Monte Carlo

Put your vehicle transmission in park, and set the emergency brake to keep the car from rolling. Lift the hood, and remove the air cleaner from the top of the carburetor by unscrewing the wing nut on the top of the air cleaner by hand.

Start your car, and allow it to idle until it warms up, and the carburetor choke opens up. Connect the tachometer to the engine by placing one of the lead wires on the negative ignition coil post, and the other lead wire to the vehicle frame. Remove the vacuum hose leading to the carburetor vacuum outlet valve, and attach the vacuum gauge to the outlet valve.

Turn the idle mixture screw, the higher of the two screws, with a screwdriver clockwise until the valve is closed completely, and then turn it back (counter-clockwise) 2 full turns. Repeat this process with the idle speed screw (near the bottom of the carburetor).

Turn the idle speed screw until the vacuum gauge reads 850 rpm's, and then turn the mixture screw clockwise about 1/4 of a turn to lean out the fuel. The idea is to reach the leanest fuel mixture possible, while allowing enough rpm's to keep the vehicle running at idle.

Look at the vacuum gauge, and see if the rpm's have changed. Turn the idle speed screw again to return the rpm's to 850 rpm's. Turn the mixture screw another 1/4 turn clockwise to continue leaning out the fuel. Continue this process until the engine is about to starve out for fuel at idle, and turn the mixture screw the opposite direction (counter-clockwise) about 1/4 turn.

Adjust the idle speed screw one more time, until the vacuum gauge reaches 850 rpm's. Remove the vacuum gauge from the carburetor, and put the vacuum hose back on the carburetor vacuum outlet. Detach the tachometer from the ignition coil, and put the air cleaner back on top of the carburetor. Secure the air cleaner to the carburetor with a wing nut, and turn the engine off.

Items you will need

  • Tachometer

  • Vacuum gauge

  • Screwdriver

 How to Adjust the Idle on a 2003 Altima

Clear Self-Learn Settings: Disconnect the battery cables, first the negative (black), then the positive. Touch the cable ends together for ten seconds. Reconnect the cables to the battery. This should clear all of the self-learn settings.

Reset the Idle Air Volume Learn Function: Turn the key on (but do not start the engine) for one second and off for ten seconds. Repeat three times. Time the intervals as accurately as possible. This should reset the idle air volume learn function.

Reset Throttle Valve Closed Position Learn: The engine and transmission must be at normal operating temperature for this procedure. Drive the car around--don't just warm it up in the driveway. Turn the ignition off and wait ten seconds. Verify that the accelerator is fully released, then turn the ignition back on and wait for three seconds. Push the pedal in and release it fully five times within five seconds. Wait for seven seconds, then push the pedal in and hold it for twenty seconds. The MIL (Malfunction Indicator Lamp) will stop blinking and come on steady. Hold the pedal in until the MIL goes out. When it goes out, release the pedal and start the engine within 3 seconds.

 How to Adjust Idle on a Nissan Pathfinder

Allow the engine to cool completely. The base idle speed must be adjusted with a cool engine on the Nissan Pathfinder. Unplug the idle air control valve located on the driver side, top of the engine, near the throttle body.

Start the engine. Turn the idle speed screw on the right side of the throttle body, located on the driver side of the engine, counterclockwise to raise the engine speed or clockwise to lower the engine speed.

Turn off the engine and plug the idle air control valve back in. Clear the stored trouble codes that were set by running the engine with the idle air control valve disconnected, using a code reader. Test drive the Pathfinder to verify that it doesn't stall at stops or with the air conditioning on.

Items you will need

  • Wrench set

  • Screwdriver set

  • Code reader

 How to Adjust the Idle on a 1989 Honda Accord DX

Start the engine and let it warm up to normal operating temperature. Listen for the cooling fan to come on twice.

Unplug the Electronic Air Control Valve (EACV): It is located on the intake, behind the fuel rail.

Check the idle speed, with all of the car's accessories turned off. It should be around 700 to 800 rpm.

Turn the ignition off. Reconnect the EACV connector. Remove either the "clock" or "back up" fuse for 10 seconds. They are located in the fuse box, in the engine bay. This will reset the ECU.

Replace the removed fuse and start the car. Check the idle speed with the car in neutral, the fan switched on "HI" and the A/C on.

Find the idle speed adjusting screw on the throttle body. It is located at the top of the throttle body, next to a vacuum line. Rotate the screw until the proper idle speed is reached.

Place the vehicle in gear and check that the idle speed remains between 700 and 800 rpm. Check the idle speed with all accessories on (lights, radio, fan, etc.), and the A/C off. The idle should remain at 700 to 800 rpm.

Items you will need

  • Flat-head (standard) screwdriver

 How to Adjust the Idle on a Toyota Rav 4

Remove the air cleaner from the top of the Toyota Rav 4 engine with an open-end wrench and set it off to the side. Locate the idle speed-control valve that is positioned at the base of the throttle body.

Detach the throttle body from the engine with a socket wrench and then separate the idle speed-control valve from the throttle body. Place the control valve on a towel or old cloth and coat the valve and throttle body with throttle body cleaner by spraying the cleaner on the inside and outside of the valve.

Clean the valve and throttle body by wiping it dry with a towel to remove any debris or oil. Spray a second coat of valve cleaner on the control valve and throttle body and use an old toothbrush to remove any remaining oil or gummy material from them. Wipe dry with a towel.

Verify there is no cloth material or any debris remaining on the parts and place the control valve back inside the throttle body. Attach the throttle body assembly back on the engine and secure with a socket wrench.

Place the air cleaner back on top of the throttle body and secure with an open-end wrench. Start the engine and verify the idle is operating better. When you are satisfied, shut off the engine.

Items you will need

  • Open-end wrench

  • Metric socket wrench set

  • Screwdriver

  • Towel or old cloth

  • Throttle body cleaner

  • Old toothbrush

 How to Adjust the Idle in a Toyota V6 3.0

Locate and pull the interior hood release lever located on the left side of the driver's side foot well. Exit the vehicle and locate the release latch underneath the center of the hood. Pull the latch upwards to raise the hood.

Locate the idle screw on the throttle body near the throttle cables. Clean any dirt or debris from the idle screw area with a shop towel.

Turn the engine on. Use a slotted screwdriver to slowly turn the idle screw while listening to the engine's idle speed. Keep turning the screw until the engine's idle is at the desired speed. Turn the engine off when finished.

Items you will need

  • Shop towel

  • Slotted screwdriver

 How to Adjust the Idle on a Hyundai

Open the hood and locate the throttle body. If you are standing at the bumper and looking down on the engine bay, it will be on your left. One one end, the throttle is connected to the fuel rail and engine. On the other end it is connected to the air intake. The throttle cable runs off from the throttle body.

Locate the throttle adjustment screw. This is actually a nut that is placed inline with the throttle cable that adjusts the tension on the cable. When the tension is too loose, your throttle valve is not opening far enough during idle and you can risk stalling the Hyundai. When the throttle cable is too tight, you are over-revving the engine and are decreasing fuel economy.

Turn on the vehicle and check the current idle speed after the vehicle has reached normal operating temperature.

Turn the throttle cable adjustment screw clockwise to tighten or counterclockwise to loosen. You should notice the idle adjust as you turn the adjustment screw.

Check the tension on the cable. There should be 1/4-inch play in the throttle cable. This should produce an idle speed of about 800 RPM. Your RPM range at idle should not drop below 500 RPM and should not rise above 1,000 RPM once the vehicle has reached normal operating temperature.

Items you will need

  • Open-end wrench

 How to Adjust the Idle on Ford Trucks

Pull the hood release lever in front of the driver's seat, open the hood and prop it up with the support arm.

Open your owner's manual to the under-hood diagram and look for the idle screw. If you do not have a manual or if you're already familiar with all the components under the hood, you can find it behind the passenger side carburetor. Its exact location varies among the different models and years of Ford trucks. It may either be a flathead or Phillips head screw, but both can be adjusted with a smaller flat head screwdriver. The screw will be visible and reachable, mounted on the end of a pipe that traces back to the carburetor, throttle or somewhere else on the engine block.

Start the engine and give it several minutes to warm up fully.

Turn the idle screw one quarter turn. If you need the engine to idle at a higher speed, turn the screw to the right. If it's running too fast, turn it to the left.

Go back to the passenger compartment and wait for about 1 minute, after which time you should see the revolutions per minute (RPM) change on the tachometer.

Repeat Step 4 and Step 5 as many times as necessary until the engine is idling at your desired speed.

Lower the hood support arm, close the hood and turn off the truck's engine.

Items you will need

  • Flat head screwdriver

  • Owner's manual for your Ford truck

 How to Adjust the Idle on a '95 Ford Mustang

Start the engine and warm it to operating temperature. In the '95 Mustang, normal operating temperature is indicated when the needle on the dash gauge is between the "R" and the "M" on the word "Normal" stamped on the gauge face. Turn the engine off.

Unplug the IAC (Idle Air Control) valve's electrical connector. The IAC in the '95 Mustang is located on the front side of the throttle body attached to the intake manifold on the passenger-side of the engine compartment near the oil filler cap. Restart the engine

Remove the black rubber plug that covers the air bleed screw located on top of the throttle body at the base of the boss that the IAC valve is bolted to. Adjust idle speed by turning the air bleed screw using a small Allen wrench until the idle speed is 700 +/- 50 rpm on the Mustang's tachometer.

Turn off engine and reinstall the IAC valves electrical connector. Disconnect the negative battery cable from the battery using a 1/2-inch wrench. Wait for 15 minutes and reinstall the negative battery cable. This will reset the on-board of computer and remove any stored trouble codes caused by running the engine with the IAC valve disconnected. Test drive the car to verify that it doesn't stall when at a stop.

Test drive the car.

Items you will need

  • Allen wrench set

 How to Adjust the Idle on a Carbureted Car

Determine whether your car has a carburetor. Most (but not all) cars built in the past decade have fuel-injection systems. If unsure, consult your car's manual.

Turn on the engine and run the car until it's at normal operating temperature.

Turn off the engine.

Remove the air filter cover, base and filter to expose the carburetor.

Find the idle adjustment screw--typically, a regular slotted screw located below the fast idle cam (a small mechanism on the side of the carburetor) that rocks on a spring-loaded hinge. The adjustment screw is attached to the throttle cable. If you pull on the throttle cable (or have someone else step on the gas pedal while you watch) you'll be able to see which screw will affect the throttle operation.

Start the car.

Tighten the idle screw one-half turn (clockwise) if the car idles roughly or conks out: screwing it in increases the idle speed.

Wait 30 seconds and then use the car's tachometer (on the dash) to check the RPMs.

Loosen the screw half a turn or until the idle is where you want it if it idles too fast. Unscrewing the idle adjustment decreases the idle speed.

Replace the air filter assembly.

Close the hood.

Items you will need

  • Air Filters

  • Auto Emergency Kits

  • Flat-head Screwdriver Sets

  • Car Manuals