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
|
| • | Check for fuel in the pressure regulator vacuum hose. |
| • | Ensure each injector harness is connected to the correct injector/cylinder. |
| • | Check items which can cause an engine to run rich, Long Term FT
is significantly in the negative range. Refer to Diagnostic Aids for
DTC P0172
. |
| • | Check items that can cause an engine to run lean, Long Term FT
is significantly in the positive range. Refer to Diagnostic Aids for
DTC P0171
. |
|
Sensor/System
|
| • | Check for conditions which cause an incorrect idle speed. |
| - | Throttle body tampering, excessive deposits or damage. |
| • | Check Crankcase ventilation valve for proper operation. |
| • | Check the throttle position (TP) sensor and related wiring. Refer
to
DTC P0123
. |
| • | Check the transaxle range switch input with the vehicle in drive
and the gear selector in drive or overdrive. |
|
Ignition
System
|
| • | Check for proper ignition voltage output using the following steps: |
| - | Clip theJ 26792
Spark
Tester to engine ground. |
| - | Connect one end of a spark plug wire to the spark tester. Leave
the other end of the spark plug wire connected 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 crisp blue
spark should be observed. |
| - | Repeat the above steps for each coil. |
| • | If adequate spark is not present at the coils, check for the following
conditions: |
| | Important: If carbon tracking is detected on a component, replace that component
and its mate.
|
| - | 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
9,840 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 check for the following: |
| | Important: If carbon tracking is detected on a component, replace that component
and its mate.
|
| - | Check the spark plugs for carbon tracking on the porcelain and pitting
on the plug wire contact. |
| - | 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
|
| • | Check 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: |
|
Additional
Checks
| Check
exhaust system for possible restrictions. Check for the following:
| • | Inspect exhaust system for damaged or collapsed pipes. |
| • | Inspect mufflers for heat distress or possible internal failure. |
| • | For possible plugged three-way catalytic converter. 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 in RPM with
little change in actual engine RPM change, indicates EMI is
present. If a condition exists, check routing of secondary
ignition wires, high voltage components (near ignition control
circuits). |
| • | Check for intake and exhaust manifold passages for casting flash. |
|
