Have you heard someone say that his car shakes at idle but smooths out while driving? Or are you facing this issue with yours? It can be scary and annoying, especially when you’ve no idea what could be the problem.
This issue isn’t always a tough nut to crack if you know the causes and how to fix them correctly. Let’s see what makes a car shake at idle and smooth out on the road.
What Causes Car Shakes At Idle But Smooths Out While Driving?
Possible reasons why your car shakes when idling but smooth when driving may include damaged motor mounts, faulty spark plugs, bad gas cap, faulty position sensors, weak oxygen sensors, loose vacuum hoses, loose battery cables, dirty throttle or bad throttle sensor.
If this is a problem you are having, diagnose the engine compartment thoroughly and fix any faulty components. Reach out to your mechanic if you cannot manage to track and cope with the problem yourself.
#1. Defective Motor Mounts.
A vehicle’s motor mounts are those features that help to hold the engine in place in its compartment such that it doesn’t move or shake when running.
The motor mounts (also called engine mounts) serve to hold the transmission and engine to the subframe while absorbing shocks and vibrations, so the driver does not feel any of such impacts when driving.
Once the motor mount breaks, it no longer holds the engine properly, resulting in uncontrollable shaking and vibration.
#2. Bad spark plugs.
The spark plug in a vehicle is used in combustion; it is what’ initiates’ the spark needed to start the air fuel mixture in the combustion chamber.
If any of the spark plugs are worn out, dirty or otherwise, they won’t do their job properly and this will cause the engine to work harder in that process. That will lead to the misfire of the engine, shaking it randomly.
#2. Clogged fuel injectors.
The fuel injectors or fuel intake system of a vehicle can become blocked with dirt. In extreme case, if you don’t unclog them, they will not supply adequate fuel needed in the combustion chamber.
This will invariably cause it to struggle to complete the process. An uneven or inadequate fuel supply leads to this vibration.
#3. Loose hoses.
Disconnected or loose vacuum hoses is common than one would imagine but often tend to go unnoticed.
Quite inadvertently, a vacuum hose can disconnect when working in a car and even driving. When it does, it’ll quaver the whole engine and in worst cases, stall the vehicle.
#4. Worn-out belts.
Dirty or worn-out timing belt is another reason why a car would shake when idle. A loose or worn-out belts will cause the engine to malfunction, resulting into it making a strange noise plus shaking it when the vehicle is idle.
Depending on the extent of the damage, that noise could go as loud as being heard when accelerating.
#6. Missing or loose gas cap.
If your gas cap is missing or loose, the vehicle’s shakes on low revs and smooths out once you hit the road with the check engine light on.
A loose or missing gas cap allows air into the fuel system, which causes the car to shake when idling but return to normal once it’s moving. A telltale sign of loose gas cap is gas smell in the cabin.
#7. Loose battery cables.
If one of your battery terminals is loose, it may not deliver enough power when idling to a point where the car vibrates. It could also be corroded.
Loose battery terminal means the engine will take longer to crank, and you might notice the headlights flicker sometimes. It could also be clicking sound when starting the engine.
#8. Dirty throttle or faulty throttle position sensor.
A car throttle body connects the fuel lines to the engine and regulates how much of the mixture goes into the path of combustion.
A dirty throttle body can therefore affect the engine performance; this will make the car vibrate and shake when stopped in gear. Sometimes, it’ll shake on idle.
If your throttle position sensor is faulty, it might send the wrong signal to the engine control unit (ECU), which will adjust accordingly no doubt. Naturally, it’ll cause the engine to vibrate.
#9. Catalytic converter problems.
A catalytic converter converts all the harmful gases emitted from the combustion chamber into an less toxic gas that’s released into the environment.
A catalyst that’s faulty or clogged, will make the car shake when stopped, and sometimes, when idling.
If the cause of your car’s problem is found to be the catalyst, you will also hear a clattering noise from it when the vehicle is idling. Besides, it will fail emission inspection.
#10. Weak or lousy O2 sensor.
Oxygen or o2 sensors measure how much air-fuel mixture is in the exhaust gas and relay this to the car computer. The car computer adjusts the air-fuel ratio that goes into the combustion chamber based on this information, and so on.
If the O2 sensor is weak, it doesn’t know what levels of air-fuel ratio are in the scrubber so it sends no or misinformation to the powertrain control module (PCM), leading to…guess what? Rough idling!
#11. Faulty fuel pressure regulator.
Another possible reason car shakes when idling and accelerating. The fuel pressure regulator regulates how much fuel goes in. Not enough and the IDM starts getting spaghetti bends in its wires and not too much or the ICD plays heck with it and squawk!! Bad news bears?
Signs that the fuel pressure regulator is bad? The car runs all glitchy even if its in gear…and you’re NOT pressing the gas pedal.
#12. Faulty idle air control valve.
The idle air control valves make sure air gets in on idle, then relating all this to the ECM. If the IAC valve is bad it sends false or no information to the ECM.
The ECM works with the information it gets, leading to too much OR too little air in the combustion chamber and making it either quiver like a toothpaste-squeezed tube, or shake like mad because it is either starving or drowning.
A bad idle air control valve will cause all kinds of headaches, not least of all delayed response when you first step on the gas and car sort of lurches back or forward instead of speeding up smoothly and quickly.
#13. Lousy Alternator.
The alternator is what recharges your battery while the engine runs and supplies power to all the electrical gadgets in your car. If it is weak, especially at very low speeds, it could be why your car vibrates when stopped at red light.
Depending upon source of problems another possibly the alternator if it looks burned out from arcing? Then that WOULD be the cause all right!! Require if this is the source of the rough idle problem and get it fixed.
What Does It Mean When Your Car Shakes While Sitting Still?
If your car shakes while it is standing still, then in most cases it implies the motor mounts are not connected to the engine or broken. The motor mounts are the components that are in charge of keeping your car’s engine attached in place within the engine compartment.
If they are broken or detached from the engine, they can no longer do the work, resulting in sporadic shaking with the potential for being so excessive as to affect the whole car.
Diagnose this problem by putting your gear on neutral (N) and waiting for a moment to see if the shaking reduces. If it does, it is a challenge from broken motor mounts and it needs to be fixed before it causes further damage.
How To Fix Car Shakes At Idle But Smooths Out While Driving
Once you establish what exactly is wrong with your vehicle’s engine and other components causing the shake, the next step is to contact a professional auto mechanic in instances that require their expert hands, and fix all the faults you can as a DIYer.
Fixing the faults listed above are not likely to cost you thousands. But if you ignore them, they will worsen. Here are our recommendations on how to handle the issues listed above.
- Have a professional mechanic fix the broken motor mounts.
- Replace or clean damaged spark plugs.
- Replace the clogged fuel injectors.
- Reconnect unfastened hoses and replace vacuum hose if it is broken
- Change that old timing belt
- Replace faulty alternator
- Change or clean that idle air control valve
- Replace bad O2 sensor
- Replace clogged or defective fuel pressure regulator
Most of the replacements outlined above are better handled by a professional auto mechanic, work that, ideally, anybody can do.
FAQs.
Q: Is it normal for a car to shake a little when idle?
It’s quite unusual for a car to shake when it’s idle, no matter how much it shakes. When your vehicle shakes while idle, something could be wrong with the engine mounts.
Also, a shaking idling vehicle could be a sign of a malfunctioning timing belt, spark plugs, or fuel injectors.
It’s best to take a moment to at least find out what could be wrong if your car shakes while stopped with the AC turned on to protect the engine from more damage. Contact a mechanic to rectify the underlying problems if you can’t sort out the problems yourself.
Q: Why does my car vibrate so much when idling?
If your car vibrates so much when idling, you likely have defective motor mounts. The vehicle’s motor mounts are to help dampen the vibration vibrations, especially if the car is idling.
Broken motor mounts won’t be able to dampen the vehicle’s vibration one bit, and you will eventually feel so much vibration when your car is idling.
If your car shakes when idle and AC is on, kindly take a moment to check if your car’s motor mounts are defective; to do that, switch the gear to Neutral (N) and listen to it for a moment. If it continues shaking, it means you have broken motor mounts.
Q: Can clogged fuel injectors cause vibration?
Of course, clogged fuel injectors can cause vibration in your vehicle. You should do your best to keep dirt from clogging your car’s fuel injectors. A clogged fuel injector will hinder the corresponding cylinder from firing properly.
Inadequate presence of fuel will make it difficult for the engine to complete each cycle of combustion properly; hence the engine begins to vibrate. If you have this kind of problem be sure to contact an expert auto mechanic.
Q: Can a bad spark plug cause the car to shake?
Another thing that can cause your car to shake upon idle is a bad or defective spark plug. This defective spark plug can cause the engine to unevenly “burn” the fuel in the cycle. When this happens, the RPMs will be fluctuating and a loud noise will arise.
Apart from the loud noise and fluctuating RPMs, the car’s engine will start to vibrate due to the force exerted by the engine trying to finish a combustion cycle due to a bad spark plug. This vibration can be felt in every part of the car.
Q. Can a bad battery make my car shake?
A defective battery will not be able to generate enough power to run the vehicle’s engine, that makes the alternator have to push harder for it to keep running.
This stress the engine exerts to keep running due to the insufficient power of the battery will eventually cause it to shake and sometimes, stall and stop.
A car battery is a component that makes the car work efficiently, but we all know the effect when the battery is defective, that could be very frustrating especially if it leaves you stranded.
Final Words
Most of the reasons why your car shakes at idle but smooths out when driving along and even the remedy to the problems have been discussed above in this article. If you have a friend who says, “My car shakes when I drive” you may want to refer him/her to read this article.
It is important to fix these mechanical faults soon enough before they grow into more complex problems. So if you are having this problem, just follow my recommendations above or call on an expert auto mechanic to diagnose and fix the problem.