Code 12 - Idle Speed Incorrect
Adjust carburetor idle speed and retest. Check all connections to carburetor, throttle actuator, and throttle kicker solenoid. Repair if necessary, and repeat test.
1) Disconnect Self-Test Input. Install vacuum "T" and gauge in throttle kicker vacuum supply line. Start engine and run at idle. Turn A/C on. Vacuum should be present. Turn A/C off. No vacuum should be present.
2) If vacuum switches, turn ignition off and go to next step. If no vacuum is present or vacuum does not switch, check vacuum line for leaks, blockage and correct routing. Repair system as necessary and go to next step.
3) Turn ignition off and apply 10 in. Hg vacuum to throttle actuator. Arm should extend and hold position while vacuum is applied. If not, repair or replace actuator and retest. If actuator operates properly, go to next step.
4) Disconnect wiring from throttle kicker solenoid and measure resistance of solenoid. If resistance is 45-90 ohms, go to next step. If not, replace solenoid and retest.
5) Check circuit resistance between throttle kicker relay connector and solenoid, and between solenoid and ground. If resistance is less than 5 ohms, go to next step. If greater than 5 ohms, repair circuit and retest.
6) Disconnect harness connector from MCU and throttle kicker relay. Check circuits for continuity between MCU connector Pin No. 12 (Red/Light Green wire) and throttle kicker relay connector, and Pin No. 20 and relay connector (Gray/Yellow wire). If resistance is more than 5 ohms, repair circuit and retest. If less than 5 ohms, go to next step.
7) Connect ohmmeter between MCU connector pin No. 12 and ground. If resistance is less than 1 k/ohm, repair short to ground in the circuit and retest. If more than 1 k/ohm, go to next step.
8) Leave MCU connector disconnected. Ensure A/C is off. Turn ignition on. Connect voltmeter across solenoid terminals (with connector on solenoid). Ground pin No. 12 of MCU connector and observe voltmeter.
9) If greater than 10 volts, verify that circuit No. 69 is not shorted to circuit No. 687. See Fig 1 . If okay, replace MCU module. If less than 10 volts, replace throttle kicker relay.