Important: When the Motronic system is operating, the idle speed is regulated by the electronically controlled idle speed controller and the CO content is monitored by the lambda probe. The idle speed and CO content are not regulated. A check is not required as part of the maintenance. However, it is advisable to have the DME fault memory regularly interrogated by a BMW service station.
Examination
Turn off all electrical consumers.
Check the air filter element and replace it if it is heavily soiled.
Warm up the engine to operating temperature. Oil temperature should be at least 60°C.
Attention: Connect measuring instruments only when the ignition is off.
Connect the speed meter in accordance with the manufacturer's operating instructions.
Note: On a six-cylinder engine, it is not permitted to connect the rev counter to terminals 1 (-) and 15 (+) of the ignition coil, since each spark plug has its own ignition coil. However, the rev counter can be roughly determined from the tachometer on the instrument panel.
Start the engine and let it idle.
Measure the number of revolutions. See the specified value below.
If the number of revolutions does not correspond to the specified value, check the tightness of the intake tract. To do this, start the engine and let it run at idle speed. Treat all seals of the intake tract (air flow meter / intake hose, intake manifold flanges) brush dipped in gasoline. When the engine speed increases, it sucks in air in loose, wetted areas. In this case, replace the corresponding seal.
Warning: Do not allow gasoline to splash onto hot parts or the ignition system. Fire hazard! Do not inhale fuel vapors - poison!
Connect the CO measuring device to the exhaust manifold by unscrewing both plug bolts from the left and right manifold. The figure shows the engine of the 316i, 318i models. "1" plug bolt of cylinders 1 and 2; "2" bolt-plug of cylinders 3 and 4. On a six-cylinder engine, the exhaust manifold is also divided into two parts; the front bolt is a plug for cylinders 1-3, and the rear bolt is a plug for cylinders 4-6. At service stations, BMW-130090 gas analyzers with a BMW-130100 adapter are used for this purpose.
Raise the car.
Disconnect the lambda probe connector on the gearbox cross beam near the catalytic converter by unscrewing the knurled nut marked "arrow".
Check CO content at idle. For specified values, see the table below.
If the CO content is elevated, the following may be the reasons: defective injectors, abnormal fuel pressure, defective coolant temperature sensor.
If the CO content is low: check the reliability of the fastening and tightness of the hoses and connections of the idle speed control system. Check the tightness of the intake tract, as described above.
Turn off the engine.
After this, check the functioning of the lambda probe.
Turn off the engine.
Clamp the vacuum hose where it connects to the fuel pressure regulator "1" with a clamp or a C-clamp. The pressure regulator is located at the end of the fuel pipe to which the injectors are connected. The figure shows a removed fuel pipe with a pressure regulator and injectors on a six-cylinder engine.
Start the engine, the CO content increases.
Connect the lambda probe connector. After this, the CO content should return to the specified value.
Turn off the engine.
Remove the clamp from the vacuum hose.
Turn off the measuring instruments.
Install the plug bolts with new gaskets into the exhaust manifold.