What is the reason for the delayed start and jerking of the Audi A4L?

[Haymitch]

Audi A4L's delayed start and jerking may be due to carbon deposits. Long-term driving at low RPM and high gears can easily lead to this situation, or it could be issues with the RPM and speed sensors. The reasons for difficulty in starting when the engine is warm are as follows: 1. Fuel injector leakage: While fuel injection is normal, 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: When starting a warm engine, fuel atomization is already normal, and no additional fuel vapor is needed. If the carbon canister continues to supply fuel vapor to the intake tract, it will cause an overly rich air-fuel mixture, making it difficult to start. 3. Fuel quality: After the warm engine is turned off for a period, the temperature in the engine compartment remains high. If the fuel is highly volatile, it can easily form high vapor pressure in the fuel rail. When this pressure exceeds the fuel supply system's pressure, vapor lock occurs, causing the fuel injector to spray overly lean fuel vapor, resulting in difficulty in starting.