The idle speed of the Mercedes A class is adjusted by the onboard ECU based on number of sensor raedings ( Lamda sensor, Hot air film sensor, air mixture).
You may be able to increase some of the parameters to increase the idle speed (for example by making the rich or lean on mixture) and this can only be done with merecedes DAS/STAR diagnostics system
You have to reprogramme the motor's ECU.
The 2008 Mercedes-Benz SLK-Class has a 6-speed manual.
The 2009 Mercedes-Benz SLK-Class has a 6-speed manual.
The 2007 Mercedes-Benz C-Class has a 6-speed manual.
The 2005 Mercedes-Benz C-Class has a 6-speed manual.
The 2005 Mercedes-Benz SLK-Class has a 6-speed manual.
The 2010 Mercedes-Benz SLK-Class has a 6-speed manual.
The 2004 Mercedes-Benz C-Class has a 6-speed manual.
The 2002 Mercedes-Benz SLK-Class has a 6-speed manual.
The 2011 Mercedes-Benz SLK-Class has a 6-speed manual.
The 2002 Mercedes-Benz C-Class has a 6-speed manual.
The 2002 Mercedes-Benz SL-Class has a 5-speed automatic.