What causes the delayed start and jerking of the Audi A4L?
2 Answers
The reasons for the delayed start and jerking of the Audi A4L are as follows: 1. Fuel injector leakage: While normal fuel injection is fine, leakage constitutes additional fuel supply. The more severe the injector leakage, the richer the air-fuel mixture becomes, leading to difficulty in starting when the engine is warm. 2. Damaged carbon canister solenoid valve: During a warm start, fuel atomization is normal and no additional fuel vapor is needed. If the carbon canister continues to supply fuel vapor to the intake manifold, it will cause an overly rich mixture, making it difficult to start. 3. Fuel quality: After the engine is shut off when warm, the engine compartment remains quite hot. If the fuel is highly volatile, it can form high vapor pressure in the fuel rail. When this pressure exceeds the fuel system pressure, vapor lock occurs, causing the fuel injector to spray overly lean fuel vapor, making it difficult to start. 4. Intake air temperature sensor: Similar to the coolant temperature sensor, the intake air temperature sensor adjusts the fuel injection quantity. However, while a faulty coolant temperature sensor causes cold start issues, a faulty intake air temperature sensor leads to difficulty in warm starts. 5. Engine carbon buildup: Carbon deposits strongly adsorb gasoline. If there is significant carbon buildup on the intake valves, throttle body, or pistons, it can adsorb some fuel, resulting in an overly lean mixture and affecting startup. This issue can also occur during cold starts.
I've done quite a bit of research on the Audi A4L's delayed start and sudden jerking issues. The most common cause is problems with the dual-clutch transmission, such as stuck solenoid valves in the valve body leading to unstable oil pressure control—when the clutch plates engage, the car lurches forward. Another frequent issue is excessive carbon buildup on the throttle body; when you press the accelerator, airflow is restricted, and the ECU responds sluggishly. Worn-out spark plugs causing poor ignition can also affect power delivery. There's also a hidden factor—turbo lag, especially during cold starts when the exhaust turbo doesn't kick in promptly, resulting in a sudden surge when it finally engages. Don't just focus on the engine; failing to replace transmission fluid on time can lead to degraded lubrication and cause similar jerking. It's best to connect to a diagnostic tool to read fault codes rather than attempting DIY repairs.
