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
|
|
Fuel System
|
| • | Inspect for fuel in the pressure regulator vacuum hose. |
| • | Test items which can cause an engine to run rich, with the long-term
fuel trim (FT) significantly in the negative range. Refer to Diagnostic Aids
for
DTC P0172 or P0175
. |
| • | Test items that can cause an engine to run lean, with the long-term
FT significantly in the positive range. Refer to Diagnostic Aids for
DTC P0171 or P0174
. |
|
Sensor/System
|
| • | Inspect for conditions which cause an incorrect idle speed. |
| - | Throttle body tampering, excessive deposits, or damage. |
| • | Test the electronic throttle control (ETC) and inspect related
wiring. |
| • | Test the exhaust gas recirculation (EGR) system for proper operation.
Refer to
DTC P0401
. |
| • | 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 spark tester. 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 spark tester, a spark should
be observed. |
| - | Repeat the above steps for each coil. |
| • | If adequate spark is not present at the coils, test for the following
conditions: |
| • | Coils--Evidence of carbon tracking or arcing, cracks in the
coils, or a resistance value outside the specified range: |
Coil Secondary Resistance
5000-8000 ohms (5K-8K ohms)
| | 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 malfunctioning.
|
| • | Spark plug wires--Inspect for the following conditions: |
| • | Evidence of cross firing |
| • | Spark plug wires--Inspect for a resistance value more than
the specified value: |
Spark Plug Wires Resistance
3280-4921 ohms/meter (1000-1500 ohms/ft) | • | Malfunctioning ignition control module. |
| • | Ignition system wiring - Loose ignition module feed or ground
connection, or damaged system wiring. |
| • | Remove spark plugs and test for the following conditions: |
| - | Burned or damaged electrodes |
| • | If spark plugs are gas or oil fouled, the cause of the fouling
must be determined before replacing the spark plugs. |
|
Engine
Mechanical
|
| - | 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: |
|
Additional Tests
|
| • | Inspect the exhaust system for a possible restriction in the following
components: |
| - | Damaged or collapsed pipes |
| - | Heat distress or possible internal failure in the muffler |
| - | Plugged three-way catalytic converter--Test for possible
plugged conditions. Refer to
Restricted Exhaust
in Engine Exhaust. |
| • | 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 or decrease in RPM with
little change in actual engine RPM indicates that EMI is present. Inspect
for incorrect routing of secondary ignition wires. Also inspect the ignition
coils for cracks, carbon tracking, or signs of arcing. |
| • | Inspect for intake and exhaust manifold passages for casting flash. |
|
