Checks
| Action
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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.
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Preliminary Checks
|
• | Refer to Important Preliminary Checks in
Symptoms |
• | Refer to Visual/Physical Checks in
Symptoms |
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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 Fuel Trim System Rich
. |
• | 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 Fuel Trim System Lean
. |
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Sensor/System
|
• | Check for conditions which cause an incorrect idle speed. |
• | Check the transaxle range switch input with the vehicle in drive
and the gear selector in drive or overdrive. |
|
Ignition System
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• | Check for proper ignition voltage output using the following steps: |
- | Clip the spark tester J 26792
to engine ground. |
- | Connect one end of a spark plug wire to the spark tester. Leave
the other end of the spark plug wire to the coil being tested. |
- | Connect one end of another spark plug wire to the other coil tower.
Connect the other end of the spark plug wire to 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 5000 - 8000 ohms (5K - 8K 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 7000 ohms (7K ohms)
| Important: Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent problem. 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 |
- | Excessive oil in combustion chamber-leaking valve seals |
• | For incorrect basic engine parts, inspect the following: |
|
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. |
• | 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 problem exists, check routing of secondary ignition wires,
high voltage components (near ignition control circuits). |
• | Check for intake and exhaust manifold passages for casting flash. |
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