Owner's Problem Description
The owner reports that the 2005 Ford Taurus engine revs by itself, with RPMs remaining high even at a stop. The vehicle accelerates without pressing the gas pedal when the brake is released. This issue can occur immediately upon starting the car. Tapping the gas pedal temporarily resolves the high RPMs. Previous attempts to fix the problem included disconnecting the cruise control cable, but the issue persists.
Professional Technical Analysis
The 2005 Ford Taurus, equipped with a 3.0L V6 engine and approximately 120,000 miles, is exhibiting a prevalent symptom of high RPMs that remain elevated during both driving and idling conditions. This issue has been reported frequently among Taurus models of this year, often linked to a malfunctioning throttle body or cruise control system. The vehicle accelerates without throttle input when the brake pedal is released, indicating a potential stuck throttle or a miscommunication within the Electronic Throttle Control (ETC) system. The cruise control system, even when disconnected, may still influence the throttle position if the throttle actuator is sticking or if there’s a fault in the accelerator pedal position sensor. Additionally, the presence of stored DTCs (Diagnostic Trouble Codes) related to throttle position could provide further insight. Given that the owner has identified a momentary fix by tapping the gas pedal, this suggests that the throttle plate may not be returning to its closed position properly due to carbon buildup or mechanical binding. Safety is a concern here; if the vehicle accelerates unintentionally, it poses a risk while driving. Therefore, a thorough inspection of the throttle body, cable, and related electronic components is vital, alongside a review of any fault codes, which can aid in pinpointing the root cause of the high RPM issue.
Possible Causes
Most common causes (ordered by frequency):
- Throttle Body Malfunction: The electronic throttle body may be sticking due to carbon buildup or mechanical binding, causing the throttle plate to remain partially open. This can result in high RPMs even when the accelerator pedal is not pressed. A thorough cleaning of the throttle body and inspection of the throttle position sensor should be performed. Typical symptoms include high idle and unresponsive throttle control. - High RPMs observed at idle, unresponsive throttle when pedal is pressed, possible stored DTCs related to throttle position.
- Cruise Control System Issue: Even after disconnecting the cruise control cable, the system may still influence throttle control if the actuator is malfunctioning. It may cause unintended acceleration due to improper throttle position feedback. Inspection of the cruise control module and wiring should be conducted. - Cruise control cable disconnected, high RPMs still occur, possible fault codes indicating cruise control issues.
- Accelerator Pedal Position Sensor Failure: A malfunctioning accelerator pedal position sensor may send incorrect signals to the PCM, causing unintended acceleration. This sensor should be tested for proper voltage output (typically 0.5V at idle and 4.5V at full throttle). - Inconsistent throttle response, possible stored codes related to accelerator pedal position.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial OBD-II Scan: Begin with a comprehensive OBD-II scan using a professional scanner or the GeekOBD APP to retrieve any stored trouble codes. Pay close attention to DTCs related to the throttle position and cruise control systems. Freeze frame data can provide critical insights into the conditions when the fault occurred.
- STEP 2 - Live Data Monitoring: Utilize the GeekOBD APP to monitor live data, focusing on the throttle position sensor readings and RPMs. Ensure the throttle position sensor is within specified voltage ranges (0.5V at idle and around 4.5V under full throttle) while observing any fluctuations that may indicate a problem.
- STEP 3 - Throttle Body Inspection: Inspect the throttle body for carbon buildup or mechanical binding. Clean the throttle body using an appropriate cleaner and ensure the throttle plate moves freely. Verify the operation of the throttle position sensor during this process.
- STEP 4 - Cruise Control and Wiring Check: After addressing the throttle body, check the cruise control module and wiring for any signs of damage or malfunction. Ensure that all connectors are secure and free from corrosion. Test the system to confirm that it no longer influences throttle position.
