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6 Reasons Your Car Is Vibrating When Idle or Stopped

Your vehicle’s dashboard is how your car communicates to you. It tells you when fuel is low, the speed you’re traveling, and even reminds you to put on your seatbelt. There’s another gauge on the dashboard that few of us notice, however, it’s there for a good reason.

It’s the RPM gauge, also known as the tachometer, that measures the rate of revolutions per minute produced by the engine. 

While idle, the engine will complete about 10 revolutions or more per second. Because of its vast speed, the gauge displays the counts as multiples of 1,000. A vehicle that is operating normally should measure at about 1,000.

When a vehicle’s RPMs fall below or are increasingly higher than normal, especially if the car vibrates when idle, something is not right.

Why Does My Car Vibrate When Idling?

Engines that operate well and idle smoothly indicate that the fuel and air provided to the engine are mixing at the optimal condition. Additionally, a well-functioning engine is able to produce the power needed to operate vital systems such as the cooling system, power steering, air conditioner, and the electrical system. 

Rough idling is often what causes a car to vibrate. If your vehicle has idling issues that cause unusual vibrations or a sluggish feeling, otherwise known as rough idling, consider it a cry for help from your car. It’s telling you that there is a component that has failed or is about to fail and needs to be addressed soon. Waiting too long could leave you stranded or stuck with costly repairs.

Rough idling issues often result in poor performance, poor fuel economy, difficulty starting, high or low RPMs, and may indicate major engine problems down the road. 

6 Causes of Rough Idle

Most vehicles today, equipped with internal computers have sensors that monitor various systems throughout the vehicle to ensure systems operate normally. The emissions system, for example, monitors the fuel combustion and exhaust system to ensure the vehicle maintains the proper emissions. If the system fails and operates beyond the predetermined parameters or the vehicle experiences rough idle, the computer will produce a code that triggers the check engine light to come on. The most common causes of a rough idle include:

1. Dirty Fuel Injectors

Vehicles today are sophisticated machines that are designed to be as fuel efficient as possible. One of the ways this is achieved is through high-pressure fuel injectors that dispense the optimal amount of fuel into the engine’s cylinder at the right time. Fuel injectors are exposed to high temperatures and fuel pressure and over time, their tiny nozzles, known as pintles may become clogged by carbon left behind from the combustion process. Obstructed fuel injectors are unable to dispense the proper amount of fuel needed for combustion or the spray pattern fails to create successful combustion, resulting in poor performance and rough idling. 

2. Worn Spark Plugs, Spark Plug Wiring, & Ignition Coil

Reasons Why You Car is Vibrating When Idle: Worn Spark Plugs

For the combustion process to succeed, there must be a spark combined with the air and fuel mixture. Spark plugs, their wiring, and the coils create the voltage to ignite in each cylinder. Spent or old spark plugs become soiled from oil or carbon deposits, greatly reducing the power created from ignition. 

By replacing your spark plugs every 30,000 to 50,000 miles you’re ensuring a sufficient spark every time. Plus, you can prevent damage to electrodes, that may result in significant damages to the ignition system. In addition to engine troubles, damaged ignition components can cause rough idling. Like spark plugs, over time the ignition coil can begin to breakdown causing misfires, a check engine light, and rough idling. 

3. Clogged Air Filters

Car Won't Start? Could be a clogged fuel filter

As you drive down the road, your engine’s air filter is trapping all kinds of contaminants that could be harmful to your engine. Over time these filters become full of dust, dirt, and other particles that prevent the proper air flow that is needed to add to the fuel mixture for combustion. A shortage of air causes the vehicle to run “rich” and may result in a rough idle as well as an increase in fuel consumption.

4. Vacuum Leak

The hoses under the hood of your car help create a vacuum for air and fuel along with the assistance of a throttle that regulates engine speed and airflow and a vacuum in the intake manifold. Over time, especially in Arizona, these rubber hoses wear out and may even develop leaks. When too much air is introduced into the fuel mixture, the engine will begin to misfire, cause rough idle, and an increase in RPMs. 

 5. Oxygen Sensor

The oxygen sensor is part of the emissions system to measure how much oxygen is in the exhaust. This information is translated to the vehicle’s computer to help calculate the ideal ratio of air and fuel for the most efficient and clean combustion process. Over time, the constant exposure to heat, carbon deposits, or age can cause the sensor to fail. When the oxygen sensor fails, the vehicle’s computer receives inaccurate information and may cause the engine to run too rich or too lean resulting in rough idle conditions. 

6. Motor Mounts

Motor mounts keep your engine attached to the car. Weak or broken mounts can’t hold the engine tight in the engine compartment and creates a vibration at idle. If the shaking subsides when the car is in Neutral, this could indicate the motor mounts are responsible for the vibrations.

Get a Professional Opinion

While dirty fuel injectors, spark plugs, wires, air filters, hoses, or sensors may be the cause of your rough idle issue, a skilled technician will need to inspect the vehicle to determine the cause. In addition to the components above, the technician will check:

  • Throttle Position Sensor
  • Mas Air Flow Sensor
  • Idle Air Control Valve
  • Engine Coolant Temperature Sensor
  • Head Gasket for leaks
  • Evaporative Emissions Control system
  • Throttle Valve
  • Fuel Pump malfunction

Rough idling is not a normal function of a vehicle. If your vehicle experiences unusual vibrations, shaking, or poor idling, take your vehicle to a trusted technician for an inspection and repair at Sun Devil Auto.