* Spark Plugs and Wires: Worn, fouled, or damaged spark plugs or ignition wires can cause misfires, especially under load (acceleration). Misfires lead to uneven combustion and jerky acceleration. Letting off the gas reduces the load, allowing the engine to run smoother despite the faulty components.
* Ignition Coil(s): Similar to spark plugs and wires, a failing ignition coil can cause misfires in one or more cylinders. This is especially common in the 4.6L Triton as it uses individual coils per cylinder.
* Mass Airflow Sensor (MAF) Sensor: A dirty or faulty MAF sensor provides inaccurate air readings to the engine's computer (PCM). This leads to an incorrect fuel mixture, causing rough running and jerky acceleration.
* Throttle Position Sensor (TPS): An inaccurate TPS signal prevents the PCM from correctly adjusting fuel delivery based on throttle position. This can lead to hesitation and jerking, especially during acceleration.
* Fuel Injectors: Clogged or failing fuel injectors can deliver inconsistent fuel to the cylinders. This will cause poor combustion and uneven power delivery.
* Crankshaft Position Sensor (CKP) or Cam Position Sensor (CMP): These sensors provide crucial timing information to the PCM. Faulty sensors can lead to poor timing and erratic running, especially under load.
* Vacuum Leaks: A vacuum leak can disrupt the airflow to the engine, negatively affecting the air-fuel mixture and causing rough running.
* Transmission Issues (Less Likely): While less likely to cause *only* jerking on acceleration and smooth running when off-throttle, transmission problems (like a slipping torque converter or worn clutch packs in an automatic) *could* contribute. This would likely be accompanied by other symptoms, such as slipping or harsh shifting.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to retrieve any stored trouble codes. This is the best starting point, as the codes will pinpoint potential problem areas.
2. Inspect Spark Plugs and Wires: Visually inspect the spark plugs and wires for damage or wear. Replace if necessary.
3. Check Ignition Coils: Inspect the ignition coils for cracks or other signs of damage. Testing with a multimeter is recommended to ensure they're providing sufficient voltage.
4. Clean the MAF Sensor: Carefully clean the MAF sensor with MAF sensor cleaner. Do not touch the sensor element.
5. Inspect Fuel Injectors (More Advanced): This typically requires a fuel pressure test and potentially injector flow testing, which may necessitate professional help.
It's important to diagnose the problem systematically. Starting with the easiest and most common causes (spark plugs, wires, MAF sensor) is often the most efficient approach. If you are not comfortable working on your vehicle yourself, it's best to consult a qualified mechanic for diagnosis and repair.
