NOX or nitrogen oxides typically elevate when combustion temperatures are high. This actually results in better performance and efficiency, but also exceeds NOX levels. EGR (exhaust gas recirculation) is used to "cool" the mixture down by replacing some of the volatile gas/air mixture with exhaust gas. A failure of the EGR valve to open, or carbon deposits in EGR ports are a common cause of high NOX. If the Mercedes does not have an EGR system, then something else is used to cool the mixture during acceleration and high speeds. I am not familiar with the system on this car , but maybe this helps find the source of the issue. Good luck.
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