What causes the Passat to shake when cold?
2 Answers
Passat shaking during cold starts can be attributed to the following reasons: 1. Excessive carbon buildup: When there is too much carbon buildup on the throttle body, fuel injectors, or intake manifold, or when there is excessive carbon inside the engine, the gasoline sprayed by the cold start injector can be largely absorbed by the carbon deposits. This results in an overly lean air-fuel mixture during cold starts, causing the engine to shake. 2. Low cylinder pressure: After prolonged use, the gaps between each cylinder liner and piston can become inconsistent. During a cold start, without proper lubrication from the engine oil, larger gaps in the cylinders can allow some high-temperature gases to leak, reducing power output. This leads to low oil pressure and cylinder pressure, resulting in insufficient power and engine shaking. 3. Faulty ignition coil: If the ignition coil fails, such as cracking and leaking electricity, it can cause insufficient or lack of spark plug ignition capability. Consequently, the air-fuel mixture in that cylinder won't ignite properly, leading to engine misfire, difficulty starting, and shaking during acceleration.
I previously experienced severe shaking during cold starts with my Passat, which turned out to be caused by severe engine carbon buildup. This car is particularly prone to carbon deposits when driven frequently in urban areas, especially around the throttle body and fuel injectors. During cold starts, the engine requires a richer fuel mixture, but carbon deposits absorb some of the gasoline, leading to insufficient fuel supply and causing the car to shake. Additionally, using low-quality gasoline worsens the problem, as carbon deposits can even clog the tiny holes in the fuel injectors. Later, I started regularly driving on highways to keep the engine at high RPMs and cleaning the throttle body every 20,000 kilometers, which significantly improved the situation. If the shaking is extremely violent—like the entire car shaking during morning starts—it might be necessary to check if the issue lies with the spark plugs or engine mounts.
