How to Fix the Idle on a 1997 Ford Explorer

by Lee Sallings

On the computer controlled 1997 Ford Explorer, the idle speed is controlled by a device called an Idle Air Control (IAC) valve. This valve acts as a controlled vacuum leak; when the computer determines that the idle needs to be higher, it opens the valve and allows more air to pass. When it needs a lower idle speed, it closes the valve and shuts off air flow. Troubleshooting an Explorer for idle speed problems is a matter of determining whether the IAC is working, and if so, where the external vacuum leak is occurring.

Step 1

Start and warm the engine to normal operating temperature according to the temperature gauge on the dash. This ensures the engine is in closed loop (computer is controlling based on sensor readings instead of preset maps) and is necessary to check and set the minimum air rate.

Step 2

Check and set the minimum air rate of the engine. With the engine off, unplug the electrical connector on the IAC valve (located on the top of the throttle body), and remove the air duct from the intake inlet. Clean the inside of the throttle body with carburetor spray to remove any carbon build up around the throttle plate. The space between the throttle plate and the throttle body is calibrated to allow only a certain amount of air to pass when the throttle is closed. Many times this cleaning alone will solve idle problems in the Explorer.

Step 3

Re-install the air duct, and start the engine. The idle speed should be 650 rpm, +/-50 rpm. If it's not, adjust the idle screw on the side of the throttle body until it is. Doing this allows the IAC valve a maximum range of control in both directions. Turn off the engine, and re-install the electrical connector on the IAC valve. Restart the engine and check idle the speed. If it is still off, go to the next step.

Turn off the engine and remove the electrical connector at the IAC valve. Restart the engine and plug the electrical connector back in. If the speed changes, the IAC valve is functioning properly and the source of the problem is an external vacuum leak. Spray the vacuum hoses and connectors and intake manifold from front to back with the carburetor spray. When the source of the vacuum leak is found with the spray, the engine speed will increase. Repair the leak as needed.

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