Can you find out what codes were retrieved? That would help a lot. The dealer will tell you and should be able to give you a printout if they are decent at documentation. The most common thing I have seen to cause asr problems is a faulty potentiometer in the throttle actuator. In that case the actuator would have to be replaced. Because i have seen this a number of times hoever, does not mean that is what is wrong. Sometimes intermmitant problems can be impossible to find and part replacement is a neccessary evil, but he may have someone looking at it who does not have a clue.
Brian

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Mercedes Benz Master Tech
ASE Master Technician
Diagnostic Technician
Owner of "Behind the Star Inc."
Raleigh NC.
www.behindthestar.com
brian@behindthestar.com