tabetha is right in what he is saying as ussual , but as you posted after he had replied that you had extended the map sensor vacuum tube are you sure this is not kinked or too soft for the vacuum that is being produced , had it in the past that when on high vacuum i.e. idle it will run rich as the map sensor is not getting to see full vac as the pipe collapses before it reaches it and so the engine management gets a little confused ?