Have you checked the voltage coming out of the 02 sensor?
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Also, time and poor gas quality will take its toll on 02 sensors.
Another item might be the engine temp sensor. I have a 300E and it's sensitive to both of these items.
Not sure if your car has fault codes but it's worth a check to see if you are getting any codes.
X/11 port on the left front fender on my car.