Why does an Audi shake and stall during cold starts?
1 Answers
Audi vehicles shaking and stalling during cold starts are primarily caused by excessive carbon buildup. Excessive carbon deposits can lead to insufficient air intake, making it difficult to start the engine or causing it to shake and stall. Carbon buildup typically occurs in several areas, including the inner walls of the throttle body, the intake valve heads, the inner walls of the intake manifold, the piston tops, and the inner walls of the combustion chamber. Below are detailed explanations: 1. Excessive carbon deposits on the inner walls of the throttle body can result in insufficient air intake, making it difficult to start the engine or causing it to stall easily at idle. Once the coolant temperature reaches the engine's normal operating temperature, the throttle opening may exceed the normal idle value, causing the ECU to repeatedly adjust the throttle valve position. This results in fluctuating idle speeds and shaking or stalling during startup. 2. Heavy carbon buildup on the intake valve heads can cause most of the fuel injected by the fuel injector during a cold start to be absorbed by the carbon deposits. This leads to insufficient fuel entering the combustion chamber, resulting in a lean mixture that is difficult to ignite. Only after multiple injections during cranking does enough fuel enter the combustion chamber for ignition. In such cases, the engine is prone to shaking and stalling during startup.
