What Causes Shaking During Automatic Transmission Startup?

[Doreen]

Below are the reasons for shaking during automatic transmission vehicle startup: 1. Fuel system obstruction: Insufficient fuel supply at low throttle causes uneven cylinder operation, resulting in shaking. 2. Dirty throttle body: Uneven intake airflow leads to operational imbalance and shaking. When excessive carbon deposits accumulate inside the engine, the cold start injector's fuel spray gets largely absorbed by these deposits, causing an overly lean fuel mixture during cold starts and making ignition difficult. 3. Damaged high-voltage wires or spark plug failure causing cylinder misfire: This creates unstable engine operation and shaking. 4. Check whether the battery voltage is within specified range. 5. Abnormal transmission operation.

[NovaFitz]

I've been driving an old automatic car for over a decade, and this jerky start issue is very common. Most likely it's due to worn engine mounts - cracked rubber causes unstable engine mounting and vibration. Spark plugs overdue for replacement can also lead to rough idling, especially noticeable when starting from a red light. Clogged fuel injectors with carbon buildup cause uneven fuel spray, so the fuel system needs cleaning. Not changing transmission fluid for too long leads to rough clutch engagement, making the car jerk. The most troublesome issue is a faulty torque converter - if accompanied by a humming noise, that's almost certainly the culprit. I suggest starting with fluid changes and engine mount replacement - cost-effective and reliable fixes.

[DeKaden]

Last time at the repair shop, the mechanic analyzed that automatic transmission shudder mainly involves two aspects: power output and transmission. On the engine side, check if the throttle body has carbon buildup or sticking, as abnormal air-fuel mixture concentration can cause jerking. If the spark plug gap exceeds 1mm, it's time to replace them, and leaking high-voltage wires can also cause cylinder misfires and shaking. For the transmission part, focus on inspecting the torque converter lock-up clutch, as clogged hydraulic valve bodies can lead to unstable oil pressure. A collapsed transmission mount is more noticeable, causing body resonance. A simple test method: with the engine warmed up, shift to D gear and press the brake - if the tachometer needle fluctuates by more than 200 RPM, it's likely an engine issue.