Checks
| Action
|
Definition:
The engine runs unevenly at idle. If severe enough, the engine or vehicle
may shake. The engine idle speed may vary in RPM. Either condition may be
severe enough to stall the engine.
|
Preliminary Check
| Refer to Important Preliminary Checks
.
|
Sensor Checks
|
| • | Check the Heated Oxygen Sensor (HO2S). |
| • | Check for silicon contamination from fuel or improperly used sealant.
The sensor will have a white powdery coating. The sensor will result in a
high but false signal voltage (rich exhaust indication). Refer to the following
items: |
| - | DTC P0131 HO2S Circuit Low Voltage Sensor 1 |
| - | DTC P0132 HO2S Circuit High Voltage Sensor 1 |
| - | DTC P0133 HO2S Slow Response Sensor 1 |
| - | DTC P0134 HO2S Circuit Insufficient Activity Sensor 1 |
| - | DTC P0137 HO2S Circuit Low Voltage Sensor 2 |
| - | DTC P0138 HO2S Circuit High Voltage Sensor 2 |
| - | DTC P0140 HO2S Circuit Insufficient Activity Sensor 2 |
| - | DTC P0141 HO2S Heater Performance Sensor 2 |
| • | Check the Throttle Position (TP) sensor. If a sticking throttle
shaft or binding linkage causes a high TP sensor open throttle indication,
the Control Module will not control the idle. Monitor the TP sensor voltage.
A scan tool or voltmeter should read less than 0.85 volts with the
throttle closed. |
| • | Check the Engine Coolant Temperature (ECT) sensor using the scan
tool to compare the engine coolant temperature with the ambient air temperature
on a cold engine. If the coolant temperature reading is more than 5 degrees
greater than or less than the ambient air temperature on a cold engine, check
for a high resistance in the coolant sensor circuit or the sensor itself.
Refer to DTC P1115 Engine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage
for the Diagnostic Aids. Refer to DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage
for the
Diagnostic Aids. |
| • | Check the Manifold Absolute Pressure (MAP) sensor response and
accuracy. |
|
Fuel System
Checks
|
| • | Check to determine if a Rich or Lean system causes the condition.
Drive the vehicle at the speed of the complaint. Monitoring the Fuel Trim
will help identify the problem. |
| - | Lean - The Long Term Fuel Trim is greater than 150. Refer to DTC P0132 HO2S Circuit High Voltage Sensor 1
for the Diagnostic Aids. Refer to DTC P0138 HO2S Circuit High Voltage Sensor 2
for the Diagnostic Aids. |
| - | Rich - The Long Term Fuel Trim is less than 115. Refer to DTC P0131 HO2S Circuit Low Voltage Sensor 1
for the Diagnostic Aids. Refer to DTC P0137 HO2S Circuit Low Voltage Sensor 2
for the Diagnostic Aids. |
| • | Check the fuel injector driver circuit. |
| 1. | Disconnect the injector harness connector at the injectors. |
| 2. | Connect an injector test lamp between the terminals of each injector
connector and note the lamp while cranking. |
If the test lamp fails to blink at any connector, it is a faulty injector
drive circuit harness, connector, or terminal.
| • | Perform the fuel injector coil test. Refer to Fuel Injector Coil Test
. |
| • | Perform the fuel injector balance test. Refer to Fuel Injector Balance Test
. |
| • | Perform a cylinder compression test. Refer to Engine Mechanical. |
| • | Check for leaking fuel injectors. Refer to Injector Circuit Diagnosis
. |
| • | Check the fuel pressure. Refer to Fuel System Pressure Test
. |
|
Ignition
System Checks
|
| • | Check the ignition output voltage using the spark tester J 26792
or the equivalent. Refer
to Enhanced Ignition System Diagnosis (Overview)
. |
| - | Remove the spark plugs. |
| - | Check for the following conditions: |
| • | Check the spark plug wires by connecting an ohmmeter to the ends
of each wire in question. If the meter reads over 30,000 ohms, replace
the wires. |
|
Additional
Checks
|
| • | Check for vacuum leaks. Vacuum leaks can cause a higher than normal
idle and low Idle Air Control (IAC) counts. |
| • | Check the IAC operation. Refer to DTC P0506 Idle Speed Low
. Refer to DTC P0507 Idle Speed High
. Refer to DTC P1509 Idle Speed High - Idle Air Control (IAC) System Not Responding
. Refer
to Fuel System Diagnosis (Central SFI)
. |
| • | Check the Control Module grounds for being clean, tight, and in
their proper locations. Refer to Component Locations. |
| • | Check the Transmission Range (TR) pressure switch assembly operation.
Refer to Transmission. |
| • | Check the scan tool to determine if the Control Module is receiving
an A/C signal. Refer to A/C Compressor Clutch Control Diagnosis
. If a problem exists with the A/C ON, check
the A/C system operation. Refer to Section 1B of the appropriate service manual. |
| • | Check for the EGR being ON while idling which will cause roughness,
stalling, and hard starting. Refer to EGR System Diagnosis (Overview)
. |
| • | Check the battery cables and ground straps. They should be clean
and secure. Erratic voltage will cause the IAC to change its position resulting
in poor idle quality. |
| • | Check the IAC Valve. Refer to Fuel System Diagnosis (Central SFI)
. |
| • | Check the A/C refrigerant pressure for being too high or for a
faulty high pressure switch. |
| • | Check the Crankcase Ventilation Valve for proper operation by
placing a finger over the inlet hole in the valve end several times. The valve
should snap back. If not, replace the valve. Refer to IAC Valve Replacement
. |
|
Engine Mechanical
Check
| Check for the following:
| • | Broken or weak valve springs. |
| • | Refer to Engine Mechanical. |
|
