Why Is My Car Shaking at Idle? Common Causes and How to Fix It

Noticing your vehicle vibrating, shaking, or rumbling when it’s stopped? If you're wondering why is my car shaking at idle, you're not alone — and the answer often points to deeper engine, ignition, or mount issues. While the car may still drive, rough idling usually signals that something’s off under the hood and needs attention.

In this blog, we’ll explore the top causes of idle shaking and how Marble Falls Auto Center can help bring back a smooth, steady engine.

Worn or Dirty Spark Plugs

One of the most common causes of shaking at idle is worn or fouled spark plugs. When one or more spark plugs misfire, it throws off the engine’s rhythm and causes noticeable vibration.

Signs of bad spark plugs:

• Engine shakes in park or at stoplights

• Decreased fuel economy

• Check engine light or rough starting

We provide full tune-ups at Marble Falls Auto Center, including spark plug inspection and replacement.

Faulty or Clogged Fuel Injectors

Your fuel injectors spray a precise amount of fuel into each cylinder. If they’re dirty or malfunctioning, your engine may run unevenly, especially while idling.

Symptoms include:

• Shaky idle or engine hesitation

• Poor throttle response

• Rough starts or misfires

We can professionally clean your injectors and restore balanced fuel delivery across all cylinders.

Why Is My Car Shaking at Idle? Common Causes and How to Fix It

Broken or Worn Engine Mounts

Your engine mounts are designed to absorb vibration and keep the engine securely in place. If they’re cracked or worn out, even a healthy engine will shake noticeably — especially when idling.

Watch for:

• Strong vibrations felt inside the cabin

• Engine shifts or moves more than normal

• Clunking sound when shifting into gear

We’ll inspect all mounts and replace any that are allowing excessive movement.

Vacuum Leak or Air Intake Problem

Modern engines rely on a precise mix of air and fuel. A vacuum leak or issue with the air intake can cause unstable idling and engine vibration.

Signs of a vacuum leak:

• Engine idle fluctuates up and down

• Hissing sound from engine bay

• Check engine light for lean condition

At Marble Falls Auto Center, we use diagnostic tools and smoke testing to track down leaks quickly.

Dirty Throttle Body or Idle Air Control Valve

A clogged throttle body or malfunctioning idle air control (IAC) valve can also cause unstable idle speed and shaking.

Symptoms include:

• Engine stalls at idle

• Unstable or surging RPMs

• Idle improves slightly when revving the engine

We offer throttle body cleaning and IAC service to smooth out engine operation.

Final Thoughts

Still wondering why is my car shaking at idle? Whether it’s spark plugs, mounts, fuel delivery, or airflow issues, rough idle is a signal that your engine needs attention. The sooner you address it, the easier and cheaper the fix.

At Marble Falls Auto Center, we specialize in diagnostics and tune-ups that restore smooth engine performance and peace of mind. Schedule your appointment today — and stop the shake.