I'm far from an expert on the intricacies of MB ASR systems but as near as I can piece together from my reading and my own ASR problems, I believe the ASR and cruise functions are integrated in many models (like yours and mine) into an electronic accelerator module. If you look at it that way, it makes sense that the system needs to know if you're hitting the brakes, say. The system is designed so that if it senses any illogical inputs, it goes into limp-home mode.

When all is working correctly, accelerator pedal input is translated electrically (not through a direct mechanical connection) into changes in the opening of the throttle plate. The reason for this is so that the ASR system can instantly disconnect that same input, if, for example, you have the accelerator floored while your wheels are on an icy patch. I believe the limp-home mode basically allows a mechanical override if the electrical communication between accelerator and throttle is lost due to malfunction.

In terms of practical advice: NO, you absolutely do not necessarily need to go to an MB dealer. You do need to have the codes pulled, or even do it yourself. The codes will lead you or a tech to the right diagnosis. In my particular case, an independent tech with the appropriate software diagnosed my bad brake pedal switch and cured the problem.

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Steve
'93 400E