Is the DSA light still on?
When you start the engine, there is a "handshake" signal
communication between the engine ECU and DSA module - the
DSA-221 code tends to be logged when the signal is of a lower
frequency than what is expected.
However, the DSA-221 fault code is also logged during an ECM
reload (together with a coolant temp sensor code) so I'm
wondering whether this has remained since you have the
software upgrade done. Ideally you want to have the ECU read
and cleared with VADIS or VIDA and then see whether the code
returns. It is possible to look at addressing this issue in the ECM
software but that should only be a last resort as it could affect
other diagnostic features as well.
In the first instance, I would recommend cleaning the idle air
control valve (with carb cleaner) on the car and also open the
throttle stop a little (without causing the engine idle speed to
rise) - is the idle speed on the car rock solid or does it fluctuate
a little?