The speedometer reading and the speed reading on the scan tool should be equal.
Before diagnosing the symptom, check service bulletins for updates.
Checks
| Action
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DEFINITION: Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down with no change in the accelerator pedal position.
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Preliminary
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• | Verify that the engine control module (ECM) grounds are clean, tight, and in the correct locations. |
• | Make sure the driver understands the operation of the transmission torque converter clutch (TCC) and the A/C compressor operation as explained in the owner's manual. Inform the customer how the TCC and the A/C clutch operate. |
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Sensor/System
| Test the heated oxygen sensors (HO2S). The HO2S should respond quickly to a change in throttle position. If the HO2S do not respond to different throttle positions, inspect for contamination from fuel, silicon, or the incorrect use of RTV sealant. The
sensors may have a white powdery coating and result in a high, but false, signal voltage, which gives a rich exhaust indication. The ECM reduces the amount of fuel delivered to the engine, causing a driveability condition.
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Fuel System
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• | Verify that the fuel injector harness is connected to the correct injector/cylinder according to the firing order. |
• | Test or inspect items that can cause an engine to run rich. For a rich condition, refer to
DTC P0172
. |
• | Test or inspect items that can cause an engine to run lean. For a lean condition, refer to
DTC P0171
. |
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Ignition System
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• | Wet down the secondary ignition system with water from a spray bottle. Wetting down the secondary ignition system may help locate damaged or deteriorated components. Look/listen for arcing or misfiring as the water is applied. |
• | Remove the spark plugs and inspect for the following: |
- | Refer to the following procedures: |
• | If the spark plugs are fouled by gas, coolant, or oil, determine the cause before replacing the plugs. Refer to the following procedures: |
- | For diagnosis of a rich condition, refer to
DTC P0172
. |
• | Inspect the ignition coil for cracks or carbon tracking. |
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Additional Checks
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• | Inspect the vacuum hoses for splits or kinks. Verify that the routing and connections are as shown on the Vehicle Emission Control Information label. |
• | Test the transmission torque converter clutch (TCC). A TCC applying too soon can cause the engine to surge or chuggle. Refer to
Symptoms - Automatic Transmission
in Automatic Transmission - Aisin (81-40LE). |
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