Rough, Unstable, Or Incorrect Idle And Stalling - Isuzu 2008MY N Series Workshop Manual

Rough, Unstable, or Incorrect Idle and Stalling

Checks
Definition:
Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in RPM.
Either condition may be severe enough to stall the engine.
Preliminary Checks
Sensor Checks
• Diagnostic System Check - Engine Controls.
• Remove the air cleaner and check for dirt, or for air ducts being plugged or
restricted. Replace as necessary.
• Inspect the ECM grounds for being clean, tight, and in their proper
locations.
• Inspect that the harness connectors are correctly connected.
• Inspect the fuel type and quality.
• Inspect the programmed fuel injector ID code for each cylinder.
• Inspect the Scan Tool Data List in this section.
• Inspect the Service Bulletin.
Inspect the engine control sensors for the following conditions. Refer to the
Scan Tool Data List in this section.
• Compare the Coolant Temperature with the Intake Air Temperature (IAT)
and Fuel Temperature (FT) parameters on a cold engine condition. If the
difference among temperature reading is more than 5°C (9°F) on a cold
engine, check for high resistance in each circuit or for a skewed sensor.
Notice: The mass air flow (MAF) sensor is heated and as a result the IAT may
indicate a higher than normal intake air temperature if the ignition switch is
being ON.
• Observe the Fuel Rail Pressure (FRP) Sensor parameter with the engine
OFF. The FRP Sensor should read 0.9 to 1.0 volt with the ignition switch
ON and engine OFF after the engine has stopped running for a minimum of
1 minute. If not, check for high resistance in each circuit or for a skewed
sensor.
• Observe the Fuel Rail Pressure parameter at idle in Neutral. The Fuel Rail
Pressure should always be within 27 to 33 MPa (3,900 to 4,800 psi) after
warm up.
• Crankshaft position (CKP) sensor is tight and the sensor rotor is not
damaged.
• Camshaft position (CMP) sensor is tight and the camshaft gear is not
damaged.
Engine Control System (4HK1)
Action
1A-349