Mercedes-Benz W210 CDI idle hunts and rail pressure fluctuates
200 CDI220 CDI270 CDI320 CDI
The W210 CDI hunts or idles unevenly - what causes it?
The most common cause is the rail pressure regulator or its leaking seals. Other causes are the leaking copper seals of the injectors and return leakage, a faulty mass air flow sensor, and the rail pressure sensor. The symptom is often worst with a cold engine.
What should the rail pressure be at idle on the W210 CDI?
On the 220 CDI the pressure should be 240-270 bar at idle. When the car hunts, the reading can jump between 180-360 bar. Pressure jumping points to the regulator, the sensor or the injectors.
What if no fault code appears?
A fault can exist without a code. Then first check the rail pressure regulator and its seals, the condition of the injectors and the mass air flow sensor. It is worth watching the pressure curve with a diagnostic tool, because an old-style test can pass a faulty sensor.
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