You may have a problem with your E/S system. It is possible that the transmission remains in Economic regardless what mode your switch is set on...

Do you experience any difference in accelerating the car when it is in E and in S? Does it start in first gear when you step on the accelerator in S? Is there any difference in shifting up gear when the transmission is switched in either E or S?

...just some thoughts...greetingz,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)