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 playOil pump inspection
Inspect the oil pump in the following procedures:
remove the oil pump. Refer to “oil pump removal and installation” .
Rotate the oil pump by hand and check that it moves
smoothly. If it does not move smoothly, replace the
oil pump assembly.
Caution
do not attempt t ...
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.
...
Use of sds diagnosis reset procedures
Note
the malfunction code is memorized in the
ecm also when the lead wire coupler of any
sensor is disconnected. Therefore, when a
lead wire coupler has been disconnected at
the time of diagnosis, erase the stored
malfunction history code using sds.
After repairing ...