Running rich is not normally a problem for the engine, yes you can get some carbon build up but nothing too bad espeshally if only going to do short distance. running lean can be lethal to your engine. - This once happened to me and the result was a hole in piston 3. This sounds like you are running a map not suitable for your injectors? I would recomend you give the people a ring who maped you car and tell them about any changes post mapping and ask them for an opinion!