Checks
| 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 Checks
|
| • | Refer to Important Preliminary Checks. |
| • | Refer to Visual/Physical Checks. |
|
Fuel
System
|
| • | Test the fuel injectors using the following tests: |
| • | Inspect for fuel in the pressure regulator vacuum hose. |
| • | Ensure each injector harness is connected to the correct injector/cylinder. |
| • | Test items which can cause an engine to run rich, long term fuel
trim is significantly in the negative range. Refer to Diagnostic Aids for
DTC P0172
. |
| • | Inspect items that can 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
|
| • | Inspect for conditions which cause an incorrect idle speed. |
| - | Throttle body tampering, excessive deposits, or damage |
| • | Test crankcase ventilation valve for proper operation. |
| • | Test the TP sensor and related wiring. Refer to
DTC P0123
. |
| • | Test the EGR system for proper operation. |
| • | Test the transaxle range switch input with the vehicle in drive
and the gear selector in drive or overdrive. |
|
Ignition
System
|
| • | Test for proper ignition voltage output using the following steps: |
| - | Clip the J 26792
Spark Tester to engine ground. |
| - | Connect one end of a spark plug wire to the J 26792
. Connect the other end of the spark
plug wire to the coil being tested. |
| - | Connect another spark plug wire between the remaining tower of
the coil being tested and ground. |
| - | Crank the engine while observing the J 26792
. A crisp blue spark should be observed. |
| - | Repeat the above steps for each coil. |
| • | If spark is not present at the coils, check for the following
conditions: |
| - | Coils--Cracks, carbon tracking/arcing, or a secondary 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
9,840 ohms per meter (3,000 ohms per ft)
| | Important: Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent condition. Ignition components will arc to ground
when a secondary component is faulty.
|
| - | Ignition system wiring--Loose ignition module feed or ground
connection, or damaged system wiring |
| • | Remove spark plugs and inspect for the following: |
| - | 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. |
|
Engine
Mechanical
|
| • | Test and inspect engine mechanical for the following: |
| - | Sticking or leaking valves |
| - | Excess oil in combustion chamber--Inspect for leaking valve
seals. |
| • | Inspect for incorrect engine parts, such as the following basic
components: |
Refer to
Symptoms - Engine Mechanical
in
Engine Mechanical.
|
Additional Checks
|
| • | Test exhaust system for possible restrictions. Inspect for the
following: |
| - | The exhaust system for damaged or collapsed pipes. |
| - | The mufflers for heat distress or possible internal failure. |
| - | For possible plugged three-way catalytic converter--Refer
to
Restricted Exhaust
in Engine Exhaust. |
| • | Inspect for faulty motor mounts. |
| • | 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, near ignition control circuits. |
| • | Inspect the intake and exhaust manifold passages for casting flash. |
|
