Twice a year or every 10,000 km (what comes first).
The engine must be warmed up to normal operating temperature, with the correct ignition timing and adjusted valve clearances (where they are regulated). The air filter must be in good condition and all electrical components (including air conditioning system, where available) must be turned off.
Carburetor
1. Connect tachometer and exhaust gas analyzer (CO meter) to the engine.
2. Run the engine to idle.
3. Check if the idle speed is within the values specified in Table of sizes and adjustment data at the end of the Guide. Adjustment is possible only on a 2V4 type carburetor. Turn the idle speed adjustment screw until the desired value is reached.
4. If the idle speed on the 2V4 carburetor is below normal, and the carburetor wiring is not damaged anywhere, you can install resistance in the control loop. This procedure is the responsibility of the BMW dealer service department.
5. Check the readings of the CO meter with those given in Table of sizes and adjustment data at the end of the Values Guide. If they do not match, turn the mixture adjustment screw (2) until they match.
L-Jetronic
1. Connect the tachometer and CO meter to the engine. BMW mechanics use a special CO tester, the probe of which is installed in the exhaust pipe, but you can use a regular tester that is inserted into the exhaust pipe. However, please note that on models with a catalytic converter (exhaust converter) no correct CO reading can be obtained from the exhaust pipe.
2. Run the engine to idle.
3. Check if the idle speed is within the values specified in Table of sizes and adjustment data at the end of the Guide. If not, remove the protective plug from the choke housing and turn the idle speed adjustment screw until the desired value is reached.
4. Check the readings of the CO meter with those given in Table of sizes and adjustment data at the end of the Values Guide. The mixture control screw is located on the airflow meter and may require a special tool to adjust (BMW № 13 1 060).
Motronic
1. Connect the tachometer and CO meter to the engine. BMW mechanics use a special CO tester, the probe of which is installed in the exhaust pipe, but you can use a regular tester that is inserted into the exhaust pipe. However, please note that on models with a catalytic converter (exhaust converter) no correct CO reading can be obtained from the exhaust pipe.
2. It is not possible to manually adjust the idle speed, since the idle air stabilization valve is actuated by the electronic control unit. If, at normal engine operating temperature, the idle speed is not as specified in Table of sizes and adjustment data at the end of the Manual values, check the air intake system for leaks, as well as the operation of the stabilizing air valve (see chapter Supply system).
3. Check the readings of the CO meter with those given in Table of sizes and adjustment data at the end of the Values Guide. If adjustment is required, remove the plug from the air flow meter...
...and turn the adjusting screw until the required value is obtained (some models may require a hex wrench). Finally, install a new protective plug.