Checking and adjusting engine idle speed and CO levels (BMW 5 Series E28)

Twice a year or every 10,000 km (whichever comes first).

The engine must be warmed up to normal operating temperature, with the ignition timing correctly set and valve clearances adjusted (where they are regulated). The air filter should be in good condition and all electrical components (including air conditioning system where fitted) must be turned off.

Carburetor

1. Connect the tachometer and exhaust gas analyzer (cO meter) to the engine.

2. Start the engine at idle speed.



3. Check if the idle speed corresponds to the values specified in Table of sizes and adjustment data at the end of the Manual. Adjustment is only possible on a 2B4 type carburetor. Turn the idle speed adjustment screw until the desired value is reached.

4. If the idle speed on the 2B4 carburetor is below normal, and the carburetor wiring is not damaged anywhere, you can install a resistor in the control circuit. This procedure is within the competence of the BMW dealer service department.



5. Compare the CO meter readings with those given in Table of sizes and adjustment data values at the end of the Manual. If they do not match, turn the mixture adjustment screw (2) until they match.

L-Jetronic

1. Connect a tachometer and a 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 gas converter) it is not possible to obtain correct CO readings from the exhaust pipe.

2. Start the engine at idle speed.

3. Check if the idle speed corresponds to the values specified in Table of sizes and adjustment data at the end of the manual. If not, remove the protective plug from the choke housing and turn the idle speed adjustment screw until the desired value is reached.

4. Compare the CO meter readings with those given in Table of sizes and adjustment data at the end of the Manual values. The mixture control screw is located on the air flow meter and may require a special tool for adjustment (BMW # 13 1 060).

Motronic

1. Connect a tachometer and a 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 gas converter) it is not possible to obtain correct CO readings from the exhaust pipe.

2. It is not possible to adjust the idle speed manually because the idle speed stabilizing pneumatic valve is actuated by the electronic control unit. If the idle speed does not correspond to the specified idle speed at normal engine operating temperature, 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 pneumatic valve (see chapter Power supply system).





3. Compare the CO meter readings with those given in Table of sizes and adjustment data values at the end of the manual. If adjustment is required, remove the plug from the air flow meter...



...and turn the adjusting screw until the desired value is obtained (some models may require a hex key). Finally, install the new protective plug.

[The original material is located on the website BMWMAN]