What causes the Jetta to jerk during cold starts like it's not getting enough fuel?
2 Answers
The reasons why the Jetta jerks during cold starts as if it's not getting enough fuel are: 1. Low engine temperature: Especially during cold starts in winter, the temperature inside the engine is insufficient, and both fuel and lubricating oil are not warm enough. Therefore, more fuel should be injected during cold starts to meet power requirements. Poor fuel atomization at low temperatures leads to reduced ignition energy, which affects performance and causes the car to shake. 2. Carbon deposits in the engine and intake tract: Since carbon deposits can absorb a certain amount of fuel, the ECU makes incorrect judgments. For example, if the computer controls the injection of 100 units of fuel-air mixture, but only 90 units actually enter the cylinder, with 10 units being absorbed by carbon deposits, even if the remaining 90 units of mixture burn completely, the required performance is still not achieved, making shaking inevitable. 3. Ignition system failure: Aging of the ignition system can weaken the ignition energy, causing the ignition coils or spark plugs to fail to ignite continuously or to experience interruptions during ignition. This intermittent ignition prevents smooth and continuous power output, resulting in jerking during acceleration. Therefore, it is important to focus on the maintenance and replacement of the ignition system during daily use. If a spark plug fails while driving, it can easily cause an engine misfire, severely affecting the engine's lifespan.
I've experienced this with my Jetta too. When starting the cold engine, the car jerks and the throttle feels sluggish, as if the fuel isn't delivering enough power. This is mostly due to fuel system issues, such as an aging fuel pump or a clogged filter, which restrict fuel flow and cause insufficient supply. Poor fuel fluidity in low temperatures can also lead to incomplete combustion. Additionally, worn or dirty spark plugs or faulty ignition coils can cause delayed ignition, worsening the jerking sensation. I had this problem during winter before, and after replacing the spark plugs and cleaning the filter, it ran much smoother. Safety shouldn't be taken lightly—unstable starts with a cold engine can affect control. It's recommended to check the fuel pump and throttle body carbon buildup as soon as possible. Regular maintenance and preheating the engine for a minute or two can significantly reduce such issues.
