BMW E36 lambda sensor fault, symptoms and replacement
What symptoms does a faulty lambda sensor cause on an E36?
Typical symptoms are fluctuating revs at idle and high fuel consumption. The fault also shows up in the emissions test. Read the fault codes before buying a sensor, because the same symptoms can have other causes.
How can I check that the E36 lambda sensor is working?
Measure the voltage from the second pin behind the sensor connector against ground. At idle the reading should be 0-1 V and fluctuating. If the reading stays steady and does not settle at a sensible level, the sensor is probably broken.
E36 lambda sensor replaced but the idle still hunts. What could be wrong?
The fault is not always in the sensor. First make sure the lambda connections are clean and dry, and check the vacuum hoses under the intake manifold. Other causes are a dirty idle control valve and a leaking accordion boot, which let extra air into the intake.
What kind of lambda sensor can I fit to an E36 and how do I handle the wires?
A Bosch lambda sensor is recommended, because cheap aftermarket sensors have lasted poorly. Most sensors have four wires: two for the heater and two for the measurement. Do not solder the sensor wires; use a ready-made connector.