Adjust the engine idle speed periodically on the engine at normal operating temperature.
To adjust the idle speed:

Engine oil and filter change
Throtile cable playTurn signal switch inspection
Inspect the turn signal switch in the following
procedures:
remove the air cleaner box. Refer to “air cleaner box removal and
installation” in section 1d .
Disconnect the left handlebar switch coupler (1).
(Yellow)
Inspect the turn signal switch for continuity wit ...
Handlebar removal and installation
Removal
Remove the following parts from the left handlebar.
left handlebar switch box (1)
handlebar balancer (2)
grip rubber (3)
clutch cable (4)
Remove the following parts from the right handlebar.
right handlebar switch box (5)
...
DTC “c28” (p1655): secondary throttle
valve actuator (stva) malfunction
Detected condition and possible cause
Detected condition
Possible cause
The operation voltage does not reach the stva.
Ecm does not receive communication signal from the
stva. Stva can not operate properly or its motor locked
Stva malfunction.
...