Idle Speed: Adjustments

Idle speed is programmed into the ECM and controlled through the idle air control (IAC) valve mounted on the throttle body. If the IAC valve is disconnected and reconnected with the engine running, idle speed may be incorrect. Reset IAC valve with the following steps:

1. Depress accelerator pedal slightly, start and run engine for five seconds.
2. Turn ignition "OFF" for 10 seconds.

Idle speed specification: 650 rpm

Minimum Idle Speed Adjustment:

MINIMUM IDLE SPEED ADJUSTMENT

Minimum idle speed is factory set with a stop screw and sealed. It should only be adjusted when installing a new IAC valve or replacing the throttle body assembly.

1. Check minimum idle speed with engine at normal operating temperature, transmission in "N" or "P" and all accessories "OFF." Connect tachometer to engine.

ALDL Connector:

2. With engine "OFF," ground DLC connector by installing a jumper wire between terminals "A" and "B."
3. Turn ignition "ON" but DO NOT start engine. Wait at least 45 seconds and disconnect IAC valve connector at throttle body. Disconnect timing set connector to put electronic spark timing (EST) in bypass mode.
4. Timing set connector is two black/white wires joined by a white connector located under the center console between the front seats. DO NOT disconnect 4-wire connector at distributor.
5. Start engine and allow system to go into closed loop. Minimum idle speed should be 650-750 rpm.
6. If adjustment is required, use an awl to pierce aluminum idle stop screw and pry out. Adjust minimum idle speed to specification.
7. Whenever minimum idle speed is adjusted, throttle position changes and throttle position sensor must be adjusted as well.
8. With engine "OFF," reconnect timing set connector and remove jumper wire from DLC. Reconnect IAC valve connector.

Throttle Position Sensor:

THROTTLE POSITION SENSOR (TPS) ADJUSTMENT

1. With ignition "OFF," disconnect TPS connector. Install three jumper wires between TPS and TPS harness connector. Turn ignition "ON" but do not start engine.
2. With a voltmeter, probe TPS connector. Connect negative lead to terminal "A" (black wire) and positive lead to terminal "B" (blue/red wire).
3. With throttle closed, voltmeter should read .42-.54 volt. If voltage is not within specification, loosen TPS mounting screws and adjust TPS until voltage is correct.
4. Tighten attaching screws and recheck voltage. Turn ignition "OFF" and restore TPS connection.