Air/Fuel Mixture: Adjustments

Prior to checking and adjusting basic CO level (idle mixture), ensure ignition timing, idle speed, valve clearances and fuel pump pressure are within specifications.
1. Connect BMW service tester or suitable tachometer to engine.
2. Connect exhaust analyzer to ports in exhaust manifold, and disconnect vacuum hose to charcoal canister or purge solenoid, leaving end of hose open.
3. Run engine until it reaches normal operating temperature, ensure that idle speed is within specifications.
4. CO reading should be 0.2 - 1.2%. If CO reading is too low, check for air leaks in intake system, oil dipstick, filler cap and engine case covers, and correct as needed.
5. Disconnect electrical connector to oxygen sensor and observe CO reading. CO reading should remain as observed in step 3. If CO reading changes when disconnecting and connecting oxygen sensor lead, check oxygen sensor circuit for opens or shorts.
6. If CO readings are not within specifications and all related control systems are operating properly, adjust basic CO level as follows:
a. Stop engine and remove concealment plug covering air flow sensor bypass volume adjusting screw (located on the bottom on the air flow sensor, near the connection to the air boot).
b. Ensure air flow sensor is properly installed, if removed, reconnect oxygen sensor lead, then start engine and run engine until it reaches normal operating temperature.
c. Ensure idle speed is within specifications, disconnect electrical connector to oxygen sensor, then adjust air volume screw as needed to obtain correct CO value.
d. Reconnect electrical connector to oxygen sensor and ensure CO reading does not change.
7. When CO level has been adjusted to specifications, stop engine, remove test equipment and reconnect vacuum hoses, then press new concealment plug into air flow sensor. The air flow sensor must be removed to install concealment plug, check CO level after installing sensor to ensure that no air leaks exist.