When you start up your car, you expect everything to run smoothly. But what do you do when you start your vehicle, and it starts vibrating and shaking?
Below we’ve highlighted some of the most common reasons for a rough idle – and what you can do to fix them.
The Basic Mechanical Breakdown
There are two main reasons that your engine might vibrate or shake while you’re idling, but the causes for these issues vary.
The first issue is an engine misfire. This occurs when your engine’s spark plug fires at the wrong time or there isn’t enough fuel or air in the combustion chamber to match the rest of the engine’s performance. If you leave this problem alone, you risk damaging your engine block, leading to you replacing your engine.
The second issue is a mounting issue. Your engine creates a lot of force, which is why the manufacturer mounts it to your vehicle’s frame, so it doesn’t move around. But if these mounts aren’t doing their job, your engine will shift around.
By the time you’re feeling it when you idle, the problem is severe enough that you shouldn’t drive the vehicle anywhere before it’s repaired.
7 Causes of Car Vibrates When Stopped or Idling
- Worn Spark plugs
- Loose or disconnected vacuum hoses
- Broken or loose engine mounts
- Worn out belts
- Damaged Fuel Pump/Fuel Injectors/Fuel Filter
- Clogged air filter
- Faulty camshaft timing
There are few problems more irritating than rough idle. But with a little know-how and expertise, you can diagnose the cause of your rough idle and have everything running smoothly again in no time.
Below is a more detailed list of the seven most common reasons why a car vibrates when stopped or at idle.
Worn Spark Plugs
One of the most common reasons for a rough idle is worn or damaged spark plugs. If you have worn spark plugs, your engine might misfire, which causes shaking or vibrations. If you have a faulty spark plug, you should have a check engine light on your dashboard, but that doesn’t always happen.
The good news is that spark plugs are cheap, but you should replace them all if one goes bad. From there, you should change your spark plugs every 80,000 to 100,000 miles to prevent this problem from cropping up again!
Loose or Disconnected Vacuum Hoses
Whether you know it or not, your vehicle is likely using vacuum hoses to power the air and fuel systems. If these hoses are torn or disconnected, the systems won’t work the way they should, and engine performance can suffer as a result.
It’s not uncommon that when a vacuum problem gets bad enough, that the engine misfires as a result. This misfire is what you’re noticing through the vibrating or shaking.
Broken or Loose Engine Mounts
Your motor mounts hold your engine in place, so it makes sense that the motor mounts might be the problem if you have a shaking or vibrating engine. Inspecting your vehicle’s motor mounts can be difficult, depending on what you drive.
One easy way to check the motor mounts is to open the engine bay and have someone rev the engine while you’re looking at it. If the engine “jumps,” then you have faulty motor mounts.
Motor mounts themselves are relatively cheap, but it can be an extensive labor process to replace them.
Worn Out Belts
There might be multiple belts on your engine, but the two that every engine has are the serpentine belt and the timing belt. If either of these belts is worn or damaged, a rough idle is a typical result.
Serpentine belts are easier to diagnose and easier to replace. Simply open the hood and identify the largest rubber belt around the front of your engine. Give it a slight tug; if it feels loose at all, that’s a problem.
From there, check for cracks or tears along the belt. If you see signs of damage, replace the belt.
For timing belts, you’ll need a more comprehensive repair, but often you’ll have a check engine light letting you know about the problem.
Damaged or Clogged Fuel Intake/Fuel Pump/Fuel Injectors/Filter
If anything is going on with your fuel system, you’ll likely have a vibrating or shaking engine. That’s because if one of the engine’s cylinders isn’t getting enough fuel, it will throw the entire balance of the engine off.
But even if you’ve identified it as a problem with your fuel system, there are a couple of different potential culprits. The first place to check should be your fuel filter. If your fuel filter is clogged, nothing will work the way it should, and it can even end up damaging other components.
From there, you should look into your fuel injectors, fuel intake, or fuel pump. Many of these issues will cause a check engine light, which can help you narrow down the problem.
Clogged Air Filter
Just like fuel is essential to your engine’s proper operation, the air is a critical component. Fortunately for you, if the intake system is the problem causing your rough idle, the problem usually originates from the air filter.
Simply pull the old air filter out and check if it’s extremely dirty. If it is, this might be your problem. Replace the air filter, reset the code, and see if the problem goes away! Air filters typically cost between $15 and $40, and most part stores will replace them for you for free.
Faulty Camshaft Timing
Engine vibrations and shaking typically means that your engine is misfiring for one reason or another. A potential reason for an engine misfire is faulty timing. If you just completed significant work on your engine, this is more common, but it’s not unheard of to have timing issues if the belt or chain is worn or damaged.
If you need to replace your timing belt, it’s relatively expensive due to the labor involved.
While it can be tempting to ignore a rough idle for a while because your vehicle is still running, this is the last thing you want to do. The longer you let the problem go, the more likely it is to develop into something more serious.
Before you give your engine a chance to break, fix the problem! If not, a problem that you could’ve fixed for a few hundred bucks might cost you a few thousand.
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Founder, owner & main author of Mechanic Base. I have been repairing cars for more than 10 years, specialized in advanced diagnostics & troubleshooting. I have also been a drifting driver and mechanic for over 7 years.