A C28 can often be fixed by cleaning and lubricating the secondary throttle linkage. A C40 is unusual. Try a reset of the ISC valve.
1) Turn the ignition switch to the OFF position.
2) Remove the seat.
3) Put the bike in dealer mode.
http://www.vstrom.info/Smf/index.php/topic,7061.0.html4) Turn the ignition switch to the ON position.
5) Turn the ignition switch to the OFF position.
6) Then, wait more than 5 seconds.
The ISC valve automatically is set at the PRE-SET position.
7) Take the bike out of dealer mode.