Idle Speed
The target idle speed is determined from two tables indexed by coolant temperature. Immediately after starting the engine, an increased idle speed is used ('Idle speed (after start)'). Approximately 20-60 seconds after engine start, the idle speed is reduced to the normal idle speed.
With larger injectors a higher quality idle may be obtained by increasing the idle speed slightly. To do this change the tables so that no values are less than your desired idle speed.
Idle Torque Reserve
Bosch ECUs have a 'torque reserve' at idle to provide idle stability.
Table values are the percentage torque in 'reserve' at idle. The ECU creates this reserve by retarding the timing.
If the torque reserve is too low then the ECU may increase idle speed to compensate. If the torque reserve is too high then the ignition will be overly retarded. As a starting point the ignition timing at idle should average out to be around TDC (0 degrees).