When you start your car, you expect everything to start up like it should and run smoothly. But what’s your course of action when you start your car and it begins to shake and vibrate?
There’s few situations more frustrating than rough idle, but there are ways to diagnose what is causing the rough idle. With a little knowledge and experience, you’ll be able to identify the cause of your rough idle and have your vehicle running smoothly again in no time.
In this article we look at some of the most common causes of rough idle – and what, if anything, can be done to fix them.
7 Causes of a Car Vibrating or Shakes When Idling
The most common reason your car is shaking at a standstill or idle is worn spark plugs or vacuum leaks. It could also be due to loose or damaged engine mounts, a worn serpentine belt, powering issues such as a bad fuel pump, or any fuel-related problems.
The first step when your vehicle shakes or vibrates while at idle is to plug in an OBD-II scanner and check for trouble codes. If you do not show any trouble codes or can’t decode the trouble codes, there are some possible causes listed below.
Here is a more detailed list of the seven most common reasons for a car vibrating at idle or standstill.
#1. Bad Spark Plugs.
One of the main reasons for a rough idle is worn out or damaged spark plugs. If you have worn plugs your engine can misfire, causing it to shake or vibrate.
A faulty plug will likely throw a check engine light, but not always.
The good news is that spark plugs are cheap, just replace them all if just one is bad; and then replace your plugs every 80k to 100k miles to avoid this problem again!
#2. Loose or Disconnected Vacuum Hoses.
Whether you realize it or not, your vehicle is likely dependent on vacuum hoses to power the air and fuel systems. If those vacuum hoses are torn or disconnected, the air and fuel systems won’t operate correctly, which can mean reduced performance from your engine.
It is possible that when a vacuum issue gets neglected for long enough, the engine can misfire, and that misfire is what you’re noticing at idle, through vibration or shaking.
#3. Broken, Loose or Damaged Engine Mounts.
The motor mounts hold your engine in place, so it follows if you have a shaking or vibrating engine, it may be an issue with the motor mounts. Depending on your vehicle, inspecting your vehicle’s motor mounts will be easy or difficult.
One way to check the motor mounts is to open the engine bay and have someone else rev the engine while you look at it. If the engine “jumps” then the mounts may be faulty.
Motor mounts are relatively inexpensive, but the labor involved can be time-consuming.
#4. Worn Belts.
There may be several belts along your engine, but every engine has a serpentine belt and a timing belt. If either of these belts are worn or damaged, a rough idle is often a result.
The serpentine belt is easier to diagnose and easier to replace. Open the hood and it will be the largest rubber belt around the front of your engine. Pull on it lightly; if it moves at all, that is a problem.
Then you should check for cracks/tears along the belt. If you see cracks or tears replace the belt.
Timing belts are a more involved repair, but you usually have a check engine light indicating you have a problem.
#5. Damaged or Clogged Fuel Intake/Fuel Pump/Fuel Injectors/Filter.
If anything is happening with your fuel system you can expect to have a shaking/vibrating engine. This is because if one of the cylinders isn’t getting enough fuel, it throws the entire balance of the engine off.
Once you determine it has something to do with your fuel system, there are a couple of potential reasons for the problem.
First, you should find your fuel filter. If your fuel filter is clogged, nothing will work correctly and it will end up damaging other parts.
Next you want to check the fuel injectors or fuel intake or fuel pump. Most of these problems will turn on a check engine light, which will really help identify the reason.
#6. Clogged Air Filter.
Just like fuel is a necessary component for the proper performance of your engine, air is an important part of the equation. If the intake system is the reason behind the rough idle, it is likely that the air filter is where the problem originated.
You simply want to pull the air filter out and see if it is incredibly dirty. If it is, there’s your problem. Replace your filter, reset the code, and see if the problem goes away! Air filters can range between $15 and $40 – and many part stores will change it for you free of charge!
#7. Faulty Camshaft Timing.
Engine shakes and vibrations often mean that your engine is misfiring for some reason. One of the reasons for engine misfires is faulty timing.
This is more common after you just did work to your engine, but it is important to know that if the timing is bad, it doesn’t matter if everything else is fine.
If you properly replace your timing belt, the labor is rather expensive.
The Basic Mechanical Breakdown
There are two main reasons your engine could shake or vibrate while idling, but entirely different meanings.
The first problem is an engine misfire. An engine misfire happens when your engine’s spark plug fires out of sequence or not enough air or fuel in your combustion chamber to match the rest of your engine’s performance.
Ignore or take too long to fix a misfire, and you run the risk of damaging your engine block and replacing your engine.
The second is a mounting issue. How an engine makes force. Hence, the manufacturer mounts the engine to the frame of the vehicle so the engine doesn’t move around, but if the mounts are not doing their job, your engine will move around.
If you are feeling this while idling, the mounting problem is severe enough to not drive it anywhere until repairs are made.
While it can be easy to ignore a rough idle for a bit since it seems the vehicle is still working, this is the last thing you want to do. The longer you let the problem persist, the more likely the problem is going to turn into a bigger issue.
Do not give your engine a chance to break or to be broken! A problem that could have been fixed for a few hundred dollars, might cost you a few thousand dollars!