Q: Shaking when accelerating and slowing down but not cruising at a constant speed

Shaking or vibrating may be caused by many different things such as faulty spark plugs, poor fuel pressure or misfires. Other things such as a faulty idle air control valve may cause the engine idle to drop below the normal idling RPM which may also cause the motor to shake or vibrate more than normal. This creates a loss of power that resonates throughout the motor additionally causing other problems with ignition and fuel timing. Anytime a misfire is caused, this causes an imbalance in the motor which will cause the motor to shake or vibrate. The other issue that may cause this type of shaking or vibration is a broken engine mount. Engine mounts are generally rubber mounted braces that hold the engine in place to the chassis of the car. When these break or become weak or faulty, this may cause the engine to vibrate heavily. Due to the many possible causes of this type of shaking or vibration, I would suggest having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.