Air/Fuel Mixture: Adjustments

Idle Mixture Screw Plug:

1. Remove carburetor to drill out idle mixture screw plug.
2. Center punch the plug and drill a hole. Thread a screw into the hole and pull on the screw to remove plug.
3. Lightly seat idle mixture screw. DO NOT overtighten. Back off mixture screw one and one half turns. Reinstall carburetor.
4. Set parking brake, place transmission in "P" or "N" and warm engine to normal operating temperature. Ensure that choke is open and leave air cleaner installed.
5. Disconnect and plug distributor vacuum hose, vapor canister purge line and EGR vacuum line. Pinch off vacuum line to hot idle compensator valve.
6. Check and adjust idle speed if needed.

Duty Cycle Test Lead:

7. Connect a dwell or duty cycle meter to test connector located on right fender well near relay box. Connect positive meter lead to test connector and negative lead to ground. Immediately before making adjustment, run engine at fast idle for one minute to heat oxygen sensor and ensure closed loop operation.
8. Set dwell meter to 4 cylinder scale and set dwell to 36~ with idle mixture screw. Duty cycle meter will read 40%. These readings are an average of the most constant variation.
9. Check and readjust idle speed if needed.
10. Turn engine "OFF" and install new idle mixture screw plug.