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 playRegulator / rectifier construction
Regulator/rectifier
Regulator/rectifier bracket
Air intake pipe (rh)
Spacer
Wiring harness
Connect
the regulator/rectifier couplers under the wiring harness
10
N·m (1.0 Kgf-m, 7.0 Lbf-ft)
...
Ecm / various sensors
Since each component is a high-precision part, great
care should be taken not to apply any severe impacts
during removal and installation.
Be careful not to touch the electrical terminals of the
electronic parts (ecm, etc.). The static electricity from
your body may damage them. ...
DTC “c21” (p0110-h/l): iat sensor circuit
malfunction
Detected condition and possible cause
Detected condition
Possible cause
C21
Output voltage is not with in the following
range.
0.15 V ≤ Sensor voltage < 4.85 V
Iat sensor circuit open or short.
Iat sensor malfunction.
Ec ...