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). The Control Module
will reduce the amount of fuel delivered to the engine causing a sever driveability
problem. Refer to the following items |
| • | 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 and/or voltmeter should read less than .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 the following items: |
|
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.
- Check the fuel injector driver circuit.
| • | Disconnect the injector harness connector at the injectors. |
| • | Connect an injector test light between the terminals of each injector
connector and note the light while cranking. |
| • | If the test light 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 Solenoid Coil Test
for the 4.3L or
Fuel Injector Solenoid Coil Test
for the 2.2L.
- Perform the fuel injector balance test. Refer to
Fuel Injector Balance Test
for the 4.3L or
Fuel Injector Balance Test
for the
2.2L.
- Check the Evaporative Emission (EVAP) control system. Refer to
Evaporative Emission Control System Diagnosis
.
- Perform a cylinder compression test. Refer to Engine Mechanical.
- Check for leaking fuel injectors.
- Check the fuel pressure. Refer to
Fuel System Pressure Test
for the 2.2L or
Fuel System Pressure Test
for the 2.2L.
|
Ignition
System Checks
|
| 1. | Remove the spark plugs. |
| 2. | 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 the following items: |
| • | Check the Control Module grounds for being clean, tight, and in
their proper locations. Refer to Component Locations in the General Information
section. |
| • | Check the Transmission Range (TR) pressure switch assembly operation.
Refer to Transmission. |
| • | 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. The IAC will not move if the system voltage
is not within 9 to 16 volts. |
| • | 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 Crankcase Ventilation System
. |
|
Engine Mechanical
Check
| Check for the following:
| • | Broken or weak valve springs. |
| • | Refer to Engine Mechanical. |
|
