Air/Fuel Mixture: Adjustments

1. Remove plug covering basic mixture adjusting screw on air flow sensor.
2. Connect suitable tachometer to engine and exhaust gas analyzer to ports in exhaust manifold, then disconnect but do not plug hose to charcoal filter.
3. Run engine until it reaches normal operating temperature, ensure that idle speed is within specifications, then note and record CO reading.
a. CO level should be specified on underhood emissions sticker or see "SPECIFICATIONS".
b. If level is too low, check for any possible air leaks between the throttle plate and the air flow meter such as oil filler, dipstick, PCV hoses and connections, and engine covers. Repair as needed.
4. Slowly tighten mixture adjusting screw while observing CO level.
5. If CO level rises as screw is tightened, check for:
a. Defective oxygen sensor,
b. Damaged or improperly connected wiring
c. Defective ECM,
d. Repair or replace as needed.
Note; If vehicle is operated with leaded fuel, oxygen sensor and catalyst must be replaced.
6. Disconnect electrical connector to oxygen sensor and adjust CO level to specifications, then reconnect sensor connector and remove test equipment.