Inspection/Test
| Action
|
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
|
| • | Observe the owners driving habits. |
|
Fuel System
|
| • | Inspect for fuel in the pressure regulator vacuum hose. |
| • | Ensure that each injector harness is connected to the correct injector/cylinder. |
| • | Inspect for any items which may cause an engine to run rich, long term
fuel trim is significantly in the negative range. Refer to Diagnostic Aids for
DTC P0172
. |
| • | Inspect for any items which may cause an engine to run lean, long term
fuel trim is significantly in the positive range. Refer to Diagnostic Aids
for
DTC P0171
. |
|
Sensor/System
|
| • | Test for conditions which cause an incorrect idle speed. |
| - | Restricted air intake system |
| • | Inspect the air intake ducts for being collapsed, damaged areas, looseness,
improper installation, or leaking especially between the mass air flow (MAF)
sensor and the throttle body. |
| • | Inspect crankcase ventilation valve for proper operation. |
| • | Inspect the throttle position (TP) sensor and related wiring. Refer to
DTC P0123
. |
| • | Monitor the 24X crank sensor and the CMP sensor signal present parameters
on the scan tool. If both are not responding, test the sensor feed circuit. Both
sensors use a separate feed circuit but are internally connected to power. Test all
CKP sensor A and CMP sensor circuits for intermittents. Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring
Systems. |
| • | Monitor the 3X parameter on the scan tool. If the 3X is not responding,
inspect the CKP sensor B and circuits for intermittents. Inspect the ignition
control (IC) circuit, IC timing control circuit, low resolution engine speed
signal circuit and the low reference circuit for intermittents. If these circuits
become open, or shorted may not set a DTC immediately, but are capable of
causing driveability complaints. Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring Systems. |
| • | Inspect the transaxle range switch input with the vehicle in drive and
the gear selector in drive or overdrive. |
|
Ignition System
|
| • | Inspect for proper ignition voltage output using the following steps: |
| 1. | Attach the J 26792
Spark
Tester to engine ground. |
| 2. | Connect the spark plug end of the spark plug wire to the J 26792
. Connect the other end of the spark plug wire
to the coil being tested. |
| 3. | Connect the spark plug end of the companion spark plug wire to ground.
The companion spark plug wire is the wire attached to the corresponding coil tower. |
| 4. | Crank the engine while observing the J 26792
. A spark should be observed. |
| 5. | Repeat the above steps for each coil. |
| • | If spark is not present at the coils, inspect for the following conditions: |
| - | Coils--Cracks, carbon tracking/arcing, or a resistance value outside
the specified range. |
Coil Resistance
5,000-8,000 ohms | - | Spark plug wires--signs of arcing, cross firing, cracks, carbon
tracking, plug boot damage, pinched, improper routing, or a resistance
value outside the specified range. |
Spark Plug Wire Resistance
9,868 ohms per meter (3,000 ohms per foot)
| | Important: : Spraying the secondary ignition wires with a light mist of water may help locate
an intermittent condition. Ignition voltage arcs to ground when a secondary
component is faulty.
|
| - | Defective ignition module |
| - | Ignition system wiring--Loose ignition module feed or ground connection,
or damaged system wiring. |
| • | Remove spark plugs and inspect for the following conditions: |
| - | Burned or damaged electrodes |
| - | Improper heat range or reach |
| • | If spark plugs are gas or oil fouled, the cause of the fouling must be
determined before replacing the spark plugs. Refer to
Spark Plug Inspection
. |
|
Engine Mechanical
|
| • | Inspect Engine Mechanical for the following conditions: |
| - | Sticking or leaking valves |
| - | Excessive oil in combustion chamber--Leaking valve seals |
| • | Inspect for incorrect engine parts, such as the following basic components: |
|
Additional
| Inspect the exhaust system for possible restrictions:
| • | Inspect the exhaust system for damaged or collapsed pipes. |
| • | Inspect the mufflers for heat distress or possible internal failure. |
| • | Test for possible catalytic converter restrictions by testing the exhaust
system back pressure. |
| • | An engine miss condition can be caused by electromagnetic interference
(EMI) on the reference circuit. EMI can usually be detected by monitoring
engine RPM with a scan tool. A sudden increase in RPM with
little change in actual engine RPM change, indicates EMI
is present. If a condition exists, inspect the routing of secondary
ignition wires, high voltage components, e.g. near ignition
control circuits. |
| • | Inspect for intake and exhaust manifold passages for casting flash. |
|
