Driving can be an enjoyable experience, although some issues can leave you baffled once they show, and it doesn’t matter if you have an automatic or manual transmission. Why does my car shake on idle but smooth out while driving?
Such an issue may cause a trip to a mechanic if the engine continues to do this, although it is better to understand what is causing your rough idle. Old spark plugs, vacuum leaks, problems with the idle air control valve, and issues with the power steering pump if the steering wheel is shaking are far more typical in a shaking car.
In addition, a more serious issue could be the engine mounts and the reason the car shudders at idle. In our guide, you can learn all the reasons that come with the question of why does my car shake in idle? By the end, you’ll be able to self-diagnose your problems and either fix the issue yourself or determine if you need to take your car to a professional mechanic. (Read Do You Have To Bleed All 4 Brakes When Changing A Caliper)
What Causes Car Shake At Idle?
A car shaking when idling and driving the car forward can occur for several reasons and may not show on the car’s computer when diagnosing issues.
While you may typically find issues with brake rotors, and your car vibrates as you push the brake pedal, it can be baffling why your car vibrates when it’s not moving. Here’s the main reasons that affect many engine parts to cause shaking at idle speed.
Defective Motor Mounts
The motor mount of a car keeps the engine stationary inside the compartment so that it won’t wobble or move while driving. The motor mounts, also known as engine mounts, keep the transmission and engine attached to the subframe while dampening vibrations and shocks so that the driver is unaware of them while the vehicle is in motion.
When your bad motor mounts wear, the engine can no longer be held securely in place, causing excessive shaking and vibration.
Bad Spark Plugs
The spark ignites the gasoline in an engine and is produced by the spark plugs in a vehicle, which plays a significant part in the combustion process.
The engine will have to apply extra pressure throughout the combustion process if any spark plugs are damaged, worn out, or unclean. As a result, the engine will misfire and shake as it can’t function properly.
Ignition coils can show similar symptoms and are related to the plugs, as these generate the power further down the electrical system.
Clogged Fuel Injectors
Over time, dirt can clog a car’s fuel intake system or injectors. The fuel system blocks obstruct the engine’s fuel delivery system and make it difficult for the combustion cycle if you don’t remove them. The engine will shudder because of the fuel supply being unequal. A clogged fuel filter or blockage near the fuel pump offers the same symptoms, yet the issue is earlier in the fuel intake system.
You can even find a problem with a gas cap stopping fuel from passing down the fuel system as a vent hole prevents a vacuum in the system.
Loose Vacuum Hose
An engine vacuum hose leak can affect many things, and here, the vacuum hoses help eliminate exhaust gases. However, if your vacuum hose is broken or loose, the vacuum leak will make it harder to empty the fuel waste, which may cause your engine to shake.
Worn Belts
Another cause of a shaking car when it is idle is a worn-out timing belt. When a vehicle idles, loose or worn-out belts can impair the proper functioning of the fans, pumps, and more in the engine compartment, thus causing shaking at idle speed.
The central belt that drives many functions is the serpentine belt, which needs checking for cuts or has stretched.
Dirty Air filter
Air filter sound is usual when the engine running. However, if dust blocks the air filter, you’ll have enough air entering the combustion chamber, creating unnatural engine movement and noise. If the airflow filter is clogged, your engine can vibrate excessively.
Average Repair Costs To Fix Why Car Shakes At Idle But Smooths Out While Driving?
Your car shakes at idle but smooths out while driving can be caused by many things, as we have seen.
Here, you can see a rough guide to the issues causing engine vibration, such as engine mounts, spark plugs, fuel injectors, and more, and a general idea of the prices you can expect from a repair shop, depending on your car model. (Read Can I Sit In My Car With The AC On)
1. Fixing Motor Mounts
When your car shakes at idle but smooths out while driving, it could be damaged motor mounts.
However, the engine will be better supported and quit shuddering once you start driving. A car’s motor mounts might cost up to $500 to replace, depending on the severity of the issue.
2. Fixing Problems with Spark Plugs
Your car may shake while idling due to a faulty spark plug. This is so that the engine’s fuel can be ignited; if the spark plug is damaged, the ignition process won’t be as effective.
Depending on the make and model of your car and the kind of spark plug you require, the cost to replace spark plugs will change. For replacement spark plugs, you can typically expect to pay between $50 and $100. However, the price could be closer to $400 if your car has a powerful engine.
3. Blocked Fuel Injectors
Over time, fuel injectors can clog up and impede fuel flow to the engine. Significantly during idle, when less fuel is fed to the engine, this can shake the engine vibrate. With such repairs, you’ll have the intake valves and throttle plate cleaned as required.
Depending on the type and model of your vehicle, the price of replacement injectors might go up to $600.
4. Broken Vacuum Hoses
A vacuum hose takes on the task of the engine to properly combust. If these hoses are damaged or loose, the engine may shake due to insufficient air.
A vacuum hose replacement typically costs between $200 and $500. Of course, your car’s make, model, and the location of the vacuum hoses will all affect how much this will cost.
5. Worn Timing Belt
For the engine valves to open and close properly, the crankshaft and camshaft must be synchronized by the timing belt.
The idle air control valve may not shake and close at the proper times if the timing belt is worn out, which might result in the car engine shaking. Timing belt replacement is one of the most costly car repairs.
Timing belt replacement might go from $300 to $500, depending on the make and model of your vehicle. However, it is one repair you need, or you could end up with a damaged engine that costs thousands to change.
6. Faulty Intake Airflow Sensor
The intake air sensor measures the air entering the engine. The engine may shake if this sensor is damaged since it does not receive accurate air temperature data. However, the components and labor cost for this repair could range from $150 to $400. (Read Coolant Reservoir Full But Car Overheating)
7. Defective Throttle Body
The amount of air injected into the engine is managed by the throttle body. If it’s broken, too much air may enter the engine, causing it to shake.
Depending on the make and model of your vehicle, the cost to replace a defective throttle body will change. However, the repair is often not too expensive. Between $200 and $400 is the typical price to replace a throttle body.
8. Damaged Fuel Intake System
Fuel is delivered to the engine by the fuel intake system. Therefore, the engine may shake if damaged because the fuel delivery may not be adequate.
Depending on the severity of the damage, a damaged fuel intake system may cost different amounts. For example, a replacement may cost several thousand dollars, but a modest repair might just cost $100 to $300.
Dirty air filters can cause the same symptoms; this is an easy swap and shouldn’t need a mechanic or an expensive bill.
Engine Shaking At Idle: FAQs
Is it normal for a car to shake a little when idle?
A car that shakes at idle, even slightly, is abnormal. When a car shakes at idle, it could be the engine mounts. An unsteady idle may be caused by malfunctioning engine components such as timing belts, spark plugs, or fuel injectors.
If your car shakes when stopped with the AC on, find out what’s wrong to avoid further damage. Call a mechanic to fix car shakes if you can’t solve the problem.
Why my car shakes when idle?
If your car shakes a lot when sitting still, its motor mounts must be replaced. The motor mounts of a car are to reduce vibrations, mainly when the car is idle. Because damaged motor mounts cannot decrease a vehicle’s vibration by default, you will soon experience a lot of vibration when your car is idle.
Check the motor mounts of your car if it vibrates while the AC is on and you are in neutral. This enables you to check if your motor mounts are damaged. If the shaking is lessened, you almost certainly have damaged motor mounts.
Can clogged fuel injectors cause vibration?
Predictably, clogged fuel injectors can make a vehicle vibrate. So, it would be best to do everything possible to prevent your car’s fuel injectors from getting clogged with dirt.
A clogged fuel injector will naturally make it more difficult for the related cylinder to ignite properly.
When a cylinder cannot fire correctly, the engine will find it challenging to finish each combustion cycle because of insufficient fuel, resulting in engine vibration.
Can a bad spark plug cause car to shake?
A bad or damaged spark plug can cause a car to shake when idle.
Faulty spark plugs create inconsistent engine fuel combustion. As a result, engine speed may vary, and the engine will be loud.
A bad spark plug causes the engine to vibrate because of the force it exerts to complete a combustion cycle. Even accumulated carbon deposits on your plugs can cause this symptom with your car’s engine. (Learn How To Fix Car Visor)
Can I replace motor mounts myself?
You can replace a broken motor mount with the tools and know-how. The cost of replacing a car’s engine varies by model and year. You must have the tools and the vehicle’s repair manual.
Do spark plugs make cars run better?
An improved driving experience will undoubtedly result from the proper spark plug installation. The new spark plugs can reduce fuel consumption by up to 30%, lead vehicles to use less fuel, and stop car vibration at idle but smooths out while driving fast.
