Idle Speed Control (ISC)
- Before idle speed/ISC duty is checked or adjusted check the following: all wires and vacuum hoses are connected securely, accelerator cable has some play, valve clearance and timing are set to specification, and all accessories are turned off.
- Warm engine to normal operating temperature. Connect spare fuse to diagnostic switch terminal. See Fig 1 . Enter self-diagnostics and check if Code 12 is present. See TESTS W/CODES article in this section. If Code 12 is present, proceed to step 3). If Code 12 is not present, see appropriate INITIAL DIAGNOSTIC PROCEDURE in TESTS W/CODES article in this section.
- Ensure idle speed and ISC duty are within specification. See ADJUSTMENTS article in this section. If idle speed and ISC duty are correct, system is operating correctly. If idle speed is correct, but ISC duty is not correct, go to step 4). If idle speed is high, go to step 5). If idle speed is low, go to step 7).
- If idle speed is correct, but ISC duty is incorrect, adjust ISC duty. See ADJUSTMENTS
article in this section.NOTE: When ISC is almost closed, check air intake system for vacuum leaks. If no vacuum leaks are present, adjust ISC duty. If ISC duty remains unchanged when adjusting screw is rotated, check wiring circuit of duty check terminal. For information on duty check terminal, see TESTS W/CODES article in this section.
- If idle speed is high, pinch upper hose on ISC solenoid closed. See Fig 1 . The ISC solenoid is located on right side of engine, near valve cover. Note if engine speed decreases. If engine speed did not decrease, go to step 7). If engine speed decreased, go to step 6).
- Turn ignition off. Disconnect electrical connector from ISC solenoid. Using ohmmeter, check resistance between ISC solenoid terminals. Resistance should be 30-33 ohms. Replace ISC if defective. If resistance was okay, check for short in Light Green/Black wire. See Fig 1 . If wiring is okay, substitute a known good ECM and recheck.
- Ensure no vacuum leaks are present in air intake system or A/C Vacuum Switching Valve (VSV). Adjust idle speed and ISC duty. See ADJUSTMENTS article in this section. If idle speed cannot be adjusted, check air valve. See AIR VALVE under IDLE CONTROL SYSTEM.
- If idle speed is low, disconnect ISC solenoid hose from air cleaner. Note if air is being drawn into hose. If no air is being drawn in, go to step 9). If air is being drawn in, adjust idle speed and ISC duty. See ADJUSTMENTS article in this section.
- Turn ignition off. Disconnect electrical connector from ISC solenoid. Using ohmmeter, check resistance between ISC solenoid terminals. Resistance should be 30-33 ohms. Replace ISC if defective. If resistance was okay, go to next step.
- Check for open in Light Green/Black wire, defective wiring connections or clogged hoses to ISC solenoid. See Fig 1 . If all are okay, substitute a known good ECM and recheck operation.