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How to Adjust Idle on a Jeep Cherokee

by David Reber

Idle adjustment sets the proper speed of engine rotation during vehicle standstill (closed throttle). Correct idle speed is important for proper engine operation and fuel economy. Idle speed also affects the function of engine-driven accessories such as the alternator, air conditioning compressor, engine cooling fan and water pump. Idle is adjustable on 1984-1986 carburetor-equipped models of the Jeep Cherokee. On 1987 and later fuel-injected Cherokee models, idle is controlled by the engine control computer and is not adjustable as part of routine tune-up and maintenance.

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.

Tip

  • It is a good idea to make sure all other engine systems are properly functioning and adjusted before adjusting idle speed. For example, fouled spark plugs or a clogged fuel filter will cause erratic idle, making idle speed adjustment difficult and ineffective.

Warnings

  • Warmed-up engines are hot. Be careful not to touch the engine itself or any components of the cooling or exhaust systems. Severe burns can result.
  • Do not wear loose-fitting clothing, jewelry or long hair around a running engine. Loose items can catch in the fan or other moving parts and cause serious injury.

Items you will need

About the Author

David Reber has been a published writer since 1991. His work has appeared in the Kansas Herpetological Society newsletter and in "Amphibian and Reptile Conservation." He teaches high-school science and maintains a menagerie of classroom animals. Reber holds a Bachelor of Science in biology from the University of Kansas and a Master of Science in education from Emporia State University.

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