Inspect timing mark indicator and crankshaft pulley notch. See Figure . Clean timing marks if necessary. Remove diagnostic connector cover, located on left strut tower. Connect tachometer to specified terminal of diagnostic connector. See Fig 1 .
Start and warm engine to normal operating temperature. Ensure idle speed is 700 RPM. Idle speed adjusting screw is located behind rubber plug on top left rear of intake plenum chamber, slightly forward of throttle position sensor. See Figure . Turn off engine and all accessories. Attach timing light to No. 1 spark plug wire.
Connect jumper wire between diagnostic connector terminals "E1" and "T". See Fig 1 . Start engine and aim timing light at crankshaft pulley. If timing is not within specification on underhood emissions label or in IGNITION TIMING SPECIFICATIONS table, loosen distributor flange hold-down bolts and rotate distributor to obtain correct ignition timing.
Tighten distributor flange hold-down bolts to 15 ft. lbs. (20 N.m) and recheck timing. Remove jumper wire from diagnostic connector and install cover.
On all models except GSi, unplug Idle Speed Control (ISC) valve connector (mounted on front of intake plenum chamber) and recheck timing. See Fig 2 . Ignition timing should be 10 degrees BTDC. If timing is not 10 degrees BTDC, check for vacuum hose leak or ISC malfunction.
Reconnect ISC connector. Turn engine off. Remove timing light and tachometer. Install diagnostic connector cap.

Fig 1: Identifying Diagnostic Connector Terminals

Courtesy of GENERAL MOTORS CORP.

Chapter Navigation

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

Base Timing