Question:

I recently acquired a pre-owned 2007 Audi A4 2.0TDI with 170HP, and unfortunately, I've encountered some issues with its performance that I am seeking to identify and address. The vehicle is overall in excellent condition, boasting an appealing exterior and interior, and has been routinely serviced, as affirmed by the previous owner, an individual of advanced age, and validated by accompanying invoices.

Upon purchase, the previous owner mentioned that the car had not been started for a period of at least one month. Upon my initial drive home, I noticed several irregularities in its operation.

During the first start of the day, the vehicle functions smoothly, with the rev needle maintaining a slightly sub-1000 RPM level and no visible emissions of white smoke from the exhaust. However, as the engine warms up (reaching temperatures between 50-60 degrees Celsius), the car begins to exhibit shaking, the rev needle fluctuates, and thick white smoke emerges from the exhaust. The engine appears to misfire and operate suboptimally at this juncture.

After a few minutes, the rev needle stabilizes, the smoke transitions from thick to thin with a bluish tinge, and the shaking subsides. This transformation occurs while the car is idling. The emitted smoke carries an unpleasant odor and irritates the eyes.

While driving, I've noticed significant vibrations throughout the vehicle when the RPMs hover slightly below or above 2000 (most noticeable in third gear). Occasionally, there's a sensation akin to sudden braking, indicative of an abrupt power loss. Notably, no warning lights on the dashboard are illuminated.

If the car is driven and subsequently restarted at a lower temperature, the aforementioned cycle recommences, starting with thick white smoke, shaking, and minor rev needle fluctuations.

I sought the expertise of a mechanic, who, based on the vehicle specifications, advised that the car might be experiencing fuel injector failure. However, he emphasized uncertainty in this assessment, noting that the engine operates satisfactorily once it reaches optimal operating temperature. He recommended observing and assessing the car's behavior over the next few days.

I am eager to gather any insights or suggestions you may have regarding the potential issue at hand.

Answer:

Possible CAuses:

1. Fuel Injector Issues:The symptoms you've described, such as white smoke, rough idle, and a loss of power, could indicate a problem with the fuel injectors. If one or more injectors are not functioning correctly, it can affect the fuel-air mixture and combustion, leading to these issues. Testing needed please refer to this - injector testing.
2. EGR (Exhaust Gas Recirculation) System:A malfunctioning EGR system can cause rough idling, smoke from the exhaust, and a loss of power. The EGR system recirculates a portion of exhaust gases back into the engine for emission control, and if it's not functioning properly, it can affect engine performance.
3. Turbocharger Issues:Problems with the turbocharger can cause excessive smoke, especially if oil is leaking into the combustion chamber. Turbocharger issues can also lead to a loss of power and a rough running engine.
4. Cooling System Problems:Overheating or incorrect temperature regulation can cause the engine to behave erratically. It's important to check the cooling system, including the radiator, thermostat, and coolant levels, to ensure proper engine temperature.
5. Air Intake or Mass Airflow Sensor:Issues with the air intake system or the mass airflow sensor can cause irregular air-fuel mixture, leading to engine problems, including rough idling and a loss of power.
6. Engine Compression or Valve Issues:Problems with engine compression or faulty valves can also lead to shaking, rough idling, and performance issues.
7. Exhaust System Issues:Any blockage or damage in the exhaust system can cause abnormal exhaust fumes and affect engine performance.

Given the variety of potential issues, it's crucial to have a professional mechanic conduct a thorough diagnosis using diagnostic tools and expertise to pinpoint the exact cause of the problems. They may perform tests, inspect relevant components, and analyze the data from the car's computer to provide a more accurate diagnosis and recommend appropriate repairs.