Mercedes-Benz W211 automatic transmission jerks when cold
Why does the W211 automatic jerk and the revs fluctuate when cold?
The most common cause is the torque converter lock-up valve (KYB valve), located on top of the transmission conductor plate. The symptom is worst when the transmission is cold or half-warm and eases as the oil warms up. The valve has no sensor, so a fault code usually appears only after a clear failure.
Can the transmission oil cause jerking in the W211?
Yes. Old oil and too low an oil level cause the same symptom, and topping up or changing the oil is often the first repair. The oils should be changed before anything else. Coolant that has got into the transmission oil is also a possible cause.
What else can be behind the jerking, and what is done after a replacement?
The alternatives are the transmission conductor plate, a worn torque converter, and the transmission and engine mounts. After the lock-up valve or another part has been replaced, the transmission adaptations (learned values) are reset with the Star diagnostic tool. Because there are many possible causes, the fault should be tracked down step by step.