What Causes Severe Shaking During Cold Start of an Old Jetta?
2 Answers
Morning cold engine shaking is mainly caused by incomplete combustion in the cylinders, leading to insufficient vehicle power and resulting in shaking. Below is more information about car startup: Precautions: Before starting the engine each time, keep the ignition key turned on for about 3 seconds before starting the engine. This allows the PP electronic throttle to perform adaptive learning and enables the fuel system to build up oil pressure before the engine starts. This not only facilitates engine startup but also reduces the occurrence of EPC light activation and engine idle shaking due to a dirty throttle. Other Causes of Shaking: Carbon deposits, weak ignition, low cylinder pressure, unqualified fuel, etc.
Recently, I also experienced cold start shaking with that old Jetta. After troubleshooting, I found quite a few issues: First, severe carbon buildup, especially clogged valves and fuel injectors affecting the air-fuel mixture ratio, which is particularly noticeable when the engine is cold. Then, the spark plugs were worn out with excessive gaps leading to insufficient ignition energy, causing the engine to shake. Additionally, the engine mounts had aged, with cracked rubber significantly reducing vibration damping. Fuel system issues also need attention—low fuel pump pressure or a clogged fuel filter can cause poor fuel delivery. A tip: before starting in the morning, turn the ignition on to let the fuel pump run for a few seconds before cranking; this can sometimes alleviate the shaking. If this persists long-term, it's best to get it checked to avoid engine damage, which would be more costly to repair.
