Before continuing, we recommend you clean your IAC valve. What you will need is a paperclip, torx screwdriver (T-25) to make adjustments and an accurate RPM gauge. If you can afford a diagnostic RPM gauge, we recommend that as the dashboard gauge isn’t exactly calibrated for tune up type of jobs. Start the car and let it warm to operating temperature. The down side to this is the heat emitted from the engine as you try to disconnect the IAC in the following instructions. But, the engine has to be warmed up. Sorry. Use a jumper wire to ground the “Test” terminal on the ALDL connector. This terminal is part of a wiring connector located just underneath the dashboard, next to the steering column. A small plate is used to cover the connector and must be removed to gain access to the terminals. With the connector exposed, push one end of the jumper wire into the “Test” terminal (B) and the other end into the “Ground” terminal (A).

Keep in mind that the ignition must be OFF so the risk of damage to the ECM is prevented. Once the terminals are shorted, turn the ignition to the ON position without starting the vehicle. Wait 30 seconds. Remove the connector from the IAC valve (located below the TPS on the passenger side of the throttle body).

Start engine. Check the RPM gauge for the proper idle speed setting (minimum air). This information can be obtained from Specifications, Tune Up Specs for any year you select. For the car we are using (1988 350 AT), the minimum air or idle speed should be a 400 RPM. I highlighted the needle on the RPM gauge as well as marked what the goal for this vehicle should be at (400 RPM).

If the speed is off, there is a torx screw on the side of the throttle body on the driver’s side. This is what needs to be turned to adjust minimum air (or idle speed). It comes from the factory with a protective metal cap over it. If the cap is still there, use a small punch to knock it out. Set the idle speed to specifications, rotating the torx screw clockwise to raise RPM, and counter-clockwise to lower RPM. Once again, the desired RPM and needle were highlighted for ease of viewing. Once the idle RPM is set, turn off the engine.

Reconnect the connector onto the IAC. Remove the ALDL jumper. Start engine. Idle speed is now once again governed by the ECM, but your idle should be smooth and steady at about 600 RPM in Drive (for unmodified cars). Before going too far, you should adjust your Throttle Position Sensor (TPS) if any adjustments were made to the idle speed. At least verify it is correct even if you didn’t make any adjustments. If you set a Check Engine light by having the IAC disconnected, ensure the engine is off, disconnect the negative battery terminal and wait 5 minutes. This should clear the ECM of all trouble codes. Reconnect the battery and drive the car for 20 minutes to allow the ECM to “relearn.” -Allan Reinike/Tom Keliher