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 optimal conditions. 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 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.
Common Causes of Car Shaking When Idle
#1. Worn Spark Plugs.
Worn-out spark plugs can lead to a misfiring engine, causing the vehicle to vibrate at idle or running speeds.
Spark plugs are threaded into each cylinder head. They ignite the air-fuel mixture that forces the piston down in the cylinder. A damaged spark plug can lead to combustion problems that produce uncontrollable shakes and vibrations. A faulty injector or basic mechanical problems with the engine can also cause this.
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.
#2. Damaged Engine Mounts
The engine or motor mount supports the engine while dampening noise and vibration. It keeps the engine and transmission away from the chassis to prevent noise and vibration from affecting the rest of the vehicle.
Many engine mounts are fluid-filled and some mounts are electronically actuated. Over time, the motor mount’s rubber insulation can wear out, or the entire component can get damaged altogether and result in excessive vibration at idle.
If left unaddressed, a damaged motor mount can also cause other problems like overstressed components and wires, friction between drive belts and pulleys, and exhaust leaks.
#3. Loose Parts.
Another common cause of vibration while idling is due to loose parts. This includes loose spark plugs, exhaust components, suspension parts, and wheel bearings. When a component becomes loose, vibrations can be felt inside the vehicle when idling. It’s important to have any loose parts replaced or repaired immediately. This will prevent further damage down the line.
#4. Faulty Alternator/Starter Motor.
A faulty alternator or starter motor can also cause your vehicle to shake or vibrate when idling. The alternator provides power to lights, audio, and climate control systems. The starter motor handles starting the engine itself. If either one fails, it can lead to shaking or vibrating at idle speeds.
#5. Clogged Air Filters.
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.
#6. 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.
#7. Fuel System Issues
Several parts in the fuel system could cause your vehicle to vibrate excessively when idle.
The first possibility is a dirty fuel injector. The fuel injector is frequently exposed to high temperatures and pressure, resulting in carbon buildup in the pintle or nozzle.
The cylinder fed by a stuck or clogged injector engine won’t receive the right amount of fuel. This can cause anything from a high-frequency shutter or shake to a mildly rough idle.
A clogged fuel filter can also create the same problem. Over time, the fuel filter can get contaminated, which can slow down the flow of fuel.
A faulty fuel pump is another probable cause of vibration at idle. This part is responsible for sending the right amount of fuel pressure and volume to the engine so that the vehicle can run properly. Typically, when a fuel pump fails so that it produces air (cavitation) and the fuel system is returnless, air bubbles will have to pass through the injectors and can cause misfires and rough idle.
A faulty fuel pump can also lead to problems like hard starting, stalling, hesitation, and misfiring if left unaddressed.
What Should You Do?
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.
If worn spark plugs are to blame, installing new ones may resolve any vibration issues. If an engine misfire is causing your car to shake then further diagnosis may be required.
This would identify which cylinder(s) are affected and why they are not firing correctly. If a faulty idle air control valve is the culprit, replacing it with a new one may stop the vibration.
There are many potential causes for your vehicle shaking or vibrating when idling. It’s important to have these issues addressed quickly to ensure that your vehicle continues running smoothly for years to come!