Car shakes violently when idle.
Shaking or vibration (https://www.yourmechanic.com/services/engine-is-shaking-pulsating-or-vibrating-inspection) 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 (https://www.yourmechanic.com/services/idle-control-valve-replacement) may cause the engine idle to drop below...