Idle Mixture Adjustment

The idle mixture screw is protected by a plug which prevents tampering during normal tune up procedures. If it is evident that idle mixture requires adjustment, remove plug as outlined under ``Concealment Plug Removal'' in the appropriate carburetor section.





4-119 2 Bbl. ENGINE EXCEPT CALIFORNIA
Engine must be at normal operating temperature with choke open and air cleaner installed during adjustment. A/C control, if equipped, must be in off position, except where noted. Disconnect and plug vacuum lines at vacuum advance and EGR valve. Using a suitable clamp, pinch vacuum hose to idle compensator.
1. Apply parking brake, block drive wheels, then position transmission in Neutral.
2. Connect tachometer to engine following manufacturer's instructions.
3. Turn mixture screw in (clockwise) until lightly seated, then back screw out 1-1/2 turns.
4. Start engine and run at fast idle until engine reaches normal operating temperature.
5. Adjust idle speed to 950 RPM (auto. transmission) or 850 RPM (man. transmission) with throttle stop screw.
6. Adjust idle mixture screw to obtain maximum idle RPM, then reset idle speed as in Step 5.
7. Turn mixture screw clockwise (leaner) until engine speed drops 50 RPM. Engine should idle smoothly at specified curb idle speed.
8. If equipped with A/C:
a. Place A/C control in ``MAX'' position and blower switch on High.
b. Momentarily open throttle to allow A/C solenoid plunger to extend, then adjust A/C idle speed to 900 RPM.
c. Turn off A/C and blower.
9. Reconnect vacuum hoses, then remove clamp from idle compensator hose.




4-119 2 BBL. ENGINE CALIFORNIA
Engine must be at normal operating temperature with choke open and air cleaner installed during adjustment. A/C control, if equipped, must be in off position, except where noted. Disconnect and plug vacuum advance, canister purge and EGR valve vacuum lines. Using a suitable clamp, pinch vacuum hose to idle compensator.
1. Apply parking brake, block drive wheels, then position transmission in Neutral.
2. Connect dwell meter to engine following manufacturer's instructions.
3. Turn mixture screw in (clockwise) until lightly seated, then back screw out 1-1/2 turns.
4. Start engine and run at fast idle until engine reaches normal operating temperature and dwell reading begins to fluctuate, indicating ``Closed Loop'' operation.
5. Adjust idle speed to 900 RPM with throttle stop screw.
6. Adjust idle mixture screw as needed, to obtain an average dwell reading of 36°. It is normal for dwell reading to fluctuate when engine is operating at idle in ``Closed Loop.'' Dwell reading specified is average of high and low dwell fluctuations.
7. Reset curb idle speed to 900 RPM.
8. If equipped with A/C:
a. Place A/C control in ``MAX'' position and blower switch on High.
b. Momentarily open throttle to allow A/C solenoid plunger to extend, then adjust A/C idle speed to 900 RPM.
c. Turn off A/C and blower.
9. Reconnect vacuum hoses, then remove clamp from idle compensator hose.