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 playContinuity check
Measure resistance across coupler “b” (between “a”
and “c” in figure).
If no continuity is indicated (infinity or over limit), the
circuit is open between terminals “a” and “c”.
Disconnect the coupler “b” and measure resistance
between couplers “a” and “b-1”.
If no continuity ...
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 ...
Transmission components
2Nd drive gear
6Th drive gear
3Rd/4th drive gear
5Th drive gear
Countershaft/1st drive gear
Driveshaft
2Nd driven gear
6Th driven gear
3Rd driven gear
4Th driven gear
5Th driven gear
1St driven gear
Gearshift cam stopper
Gearshi ...