NOTE: Engine idle set RPM should be tested and recorded when vehicle is first brought into shop for testing. This will assist in diagnosing complaints of engine stalling, creeping, and hard shifting on vehicles equipped with automatic transmissions. Curb idle speed on 2.5L and 4.0L are controlled by electronic control unit and are not adjustable.

Using a tachometer, connect Red tachometer lead to negative terminal of coil and Black lead to ground.
Turn selector switch to appropriate cylinder position of engine being tested. Start engine and warm to operating temperature.
Turn tachometer RPM switch to 1000 RPM position.
With engine at operating temperature, momentarily open throttle and release to ensure there is no binding in linkage and throttle lever is fully against its stop.
Note engine RPM. See CURB IDLE SPEED table. If engine RPM is not within specification, see appropriate TESTS W/CODES article for 2.5L and 4.0L and see ADJUSTMENTS article for 4.2L and 5.9L.

CURB IDLE SPEED

Application		Idle RPM
2.5L, 4.0L & 4.2L
50 States		680
High Altitude		700
5.9L		600

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Idle Rpm Test

Use the Manual With the Right Hardware

When to See a Mechanic

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