A-170 CDI (Semi Automatic) Cold start problem

All of a sudden, when I start my A Class from cold, it starts ok but then stalls within a few seconds and continues to do so until warm,
but even then when pulling away it is no longer as responsive as it was. It has been in to two Mercedes dealers who say it is not registering any fault codes and they cannot find anything wrong with it. Before I spend any more money on further diagnostic work, has anyone else experienced the same problem? If so I would really appreciate some feedback. Thanks. :?
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