TEST 1 (Dwell Fixed Under 10 Degrees)

Check vacuum hose connection at idle switch. See Figure and Fig 1 . If okay, disconnect idle switch connectors and run engine at part throttle. Note dwell reading. If dwell is under 10 degrees, go to next step. If dwell varies, replace idle switch.

Fig 1: Locating Emission Control Components
Courtesy of ISUZU MOTOR CO.
If dwell is under 10 degrees, check for shorted or grounded MAP sensor and idle switch wires from ECM connector. If wiring is okay, run engine at part throttle and choke engine. If dwell increases, go to step 4). If dwell does not change, disconnect O2 sensor, and note dwell reading.
If dwell increases, replace O2 sensor. If dwell is less than 10 degrees, check for grounded Violet wire to ECM connector terminal C45-8. See Fig 2 . If wire is not grounded, replace ECM.

Fig 2: Locating ALDL & ECM Connectors
Courtesy of ISUZU MOTOR CO.
If dwell reading increased in step 2), check for intake vacuum leak, exhaust leak before O2 sensor and improper vacuum hose routing. If no leaks are found, check mixture control (duty) solenoid. See MIXTURE CONTROL (DUTY) SOLENOID under FUEL CONTROL . If mixture control solenoid is okay, repair or replace carburetor.