Based on the symptoms you described, it seems like there are several potential issues contributing to the rough idle and poor acceleration in your 2006 Audi A4 2.0T Quattro. The codes you mentioned (P2539 for the low-pressure fuel pump sensor and the camshaft position sensor code) can be helpful indicators of potential problems. Let's break down the possible causes:
Low Pressure Fuel Pump and Sensor
Since you've already replaced the low-pressure fuel pump and sensor on the fuel rail, it's possible that there's still an issue with the new pump, or there might be a problem with the fuel lines or connections causing a loss of fuel pressure.
Camshaft Position Sensor
The camshaft position sensor is crucial for engine timing and proper fuel injection. If it's malfunctioning or sending incorrect signals, it can lead to rough idling and performance issues. Make sure the sensor is properly connected and functioning. If necessary, replace it with a genuine or high-quality OEM sensor.
Fuel System Issues
Beyond the low-pressure fuel pump and sensor, there could be other problems in the fuel system, such as a faulty high-pressure fuel pump, fuel pressure regulator, or fuel injectors. A comprehensive inspection of the entire fuel system might be necessary.
Vacuum Leaks
Vacuum leaks can lead to rough idling and poor performance at low RPMs. Inspect all vacuum hoses, connections, and intake manifold gaskets for leaks.
Throttle Body
A dirty or malfunctioning throttle body can cause hesitation during acceleration. Cleaning or, if necessary, replacing the throttle body might help.
Air Intake System
Ensure the air intake system is clean and free from obstructions, including the air filter.
Exhaust System
Check for any exhaust leaks or restrictions that could affect engine performance.
Considering the issues you're facing with losing fuel pressure and difficulty starting, there could be an underlying problem with the fuel delivery system. It might be best to take the car to a qualified Audi technician or mechanic who can perform a thorough diagnosis using specialized equipment. They will be able to pinpoint the exact cause of the rough idle and performance issues and provide an appropriate solution.
As always, when dealing with complex automotive issues, it's essential to approach troubleshooting systematically and avoid replacing parts without proper diagnosis to prevent unnecessary expenses.
