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What causes rough idle in a car: Everything You Need To Know!

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Have you noticed your car making a funny noise whenever you turn on the engine? Do passengers complain about a bumpy shaky ride?  Have you noticed that it will not keep a consistent speed? This is known as rough idling and it may be a sign of a serious problem. 

Auto Repairs Are EXPENSIVE

What is idling?

A car’s idle speed is determined by the revolutions per minute of the engines’ crankshaft. When a vehicle has enough power to operate components like the steering and the alternator, but not enough to move the vehicle itself it is idling. When your car is idling, it should sound and feel smooth. If it skips or slips, you may have a problem. The average sedan can have an idle speed of anywhere between 600 and 1000 RPMs.


Rough idling may mean anything from a minor problem to a problem that could ruin the engine of your car. Although you should always take your automobile to a professional garage when it is rough idling, there are a few things you may want to know about the potential problems before you talk to a mechanic. 


Incorrect Idle Speed

Sometimes a car can have a rough idle simply because it is set to the wrong idle speed. Your vehicle has a component in it called an idle air control valve which regulates the engines idle speed. A professional mechanic can fix the setting for you. After they adjust the speed, you should not have any problems, but if the car starts to idle again, you will want to have the engine looked over at a garage.

Sometimes the idle control valve will need to be replaced. A new valve and its installation will cost you anywhere from $120 to $500. The majority of the cost is for the part as it is very simple work for a mechanic.


Damaged Plugs

Spark plugs initiate the electric spark that allows an engine to burn fuel. When spark plugs become corroded or otherwise damaged, or if they are not installed properly, you may hear your car emitting a noise that sounds like slipping or straining. The car may also idle at a lower speed than it should. Damaged plugs can cause a multitude of problems in your engine. It can even cause an engine fire. 


If you are fairly mechanical yourself, you should be able to replace your car’s spark plugs. A vehicle may have anywhere from 2 to 6 spark plugs. The parts themselves can cost anywhere from $16 to $100. You will probably need to replace them every couple of years.


An incorrectly installed spark plug can cause a multitude of problems. If you think you may not know what you are doing it is a good idea to go to an auto body shop. It normally takes under an hour for a professional mechanic to replace spark plugs. The cost of labor can be anywhere from $40 to $150 an hour.  


Electrical Parts Failure

If your ignition or any of the many parts that make up the component fails, you may experience rough idling. The problem is likely to get worse as the speed of the rotations per minute increases. The ignition control module is the part that is most likely to cause an idling problem. This module controls the fuel mixture and ignition timing. It is also responsible for monitoring the emissions that your car makes. 


When an ignition control module goes bad, you will need to have it replaced by a professional mechanic who is well versed in repairing your kind of car. The cost to replace the module will generally run between $317 and $437.


The Oxygen Sensors are Dirty

The oxygen sensors are designed to monitor the amount of unburned oxygen the exhaust contains as it exits your engine. The engine’s computer will then use those statistics to determine how much fuel needs to be released into the engine. The sensors should help the car’s engine maintain proper emissions. It is fairly easy to tell when this happens. Not only will your car idle roughly, but the check engine light should come on. You may also fail an emissions test.


It is important to clean your oxygen sensors. There are products you can buy to clean the sensors that you can obtain at any autobody store. The sensors are small and it can be difficult to locate, so when you look for it you should use goggles and gloves. 


You will then need to lift the car. Your car’s instruction manual should have a diagram that contains the precise location of the oxygen sensors. Your car will have two of these sensors, one sits in front of the catalytic converter, and another that is located in the car's exhaust manifold. It will resemble a spark plug.


In order to remove a sensor, you will have to spray it with WD40 or a similar product and let it sit for a while. You can remove the sensor with a wrench. Once it is removed, you will want to soak it overnight in gasoline to clean it. Make sure that you immerse the sensor in gasoline that is in a bucket with a lid. When you remove the plug, you should wipe it down completely with a cloth. After you put everything back together, you should turn your car on. If the engine light is still on, you will need to take your car to a mechanic. 


If you need a new sensor, it will cost you anywhere from $20 to $100. If you take it to a mechanic for replacement it can cost as much as $200. 

The Airflow Sensor is not Working 

A mass airflow sensor is a part of an automobiles fuel injection system. You will find it between the air filter and intake manifold. The MAF tracks the amount of air that comes into the engine. Rough idling may be one of many symptoms that your airflow sensor is not working. Your engine may also stall out if you do not pay attention to this important component.


A new airflow sensor can cost around $240 and there is a good chance you will have to replace it during the lifespan of your car. The good news is that it only should take a mechanic about an hour to do the work, so the labor should cost around $60.


The Fuel Filter or Fuel Pump is Clogged 

The function of the fuel pump is to transport fuel from the gas tank to the fuel injectors. If it becomes clogged, the engine will not get enough fuel to run. In addition to rough idling, you may also notice that your car may stall out often and it may be slow to accelerate. 


Similar results can occur if the fuel filters are clogged. The filter captures adulterants that are in the fuel of the car. They must be changed occasionally and if they are not, it may cause the car to idle.


Getting your fuel pump injectors cleaned will run you about $50 to $80. If you need the fuel pump replaced, it will be very expensive and with labor, it can cost anywhere from $638 to $837. If everything else in your car is running perfectly, it may be worth it to have the pump replaced. If your car is suffering from any other damage or just old age, you may want to think about replacing it. 


It is very important to clean your fuel filters or replace them on a regular basis. Some fuel filters are made of paper or nylon. When these kinds of filters get dirty, it is in your best interest to replace them as they will not be able to withstand cleaning. 


If you have metal filters, you may be able to clean them. To clean the filters, you have to remove them from the car. In order to do this, you must disconnect your battery and relieve the pressure in your fuel pump. In order to do this, you must locate the fuse in your fuel pump and remove it. Your owner’s manual should show you where this fuse is located. 


Once you have removed the fuse, start your engine and let it run for one or two minutes. You will then want to turn off the engine and disconnect the negative battery cable. 


Use your owner’s manual to locate the fuel filter. It should be between the engine and the gas tank. You may have to jack up the car in order to do this. Once you have located the fuel filter,  detach the fuel lines from it. Gas will spill when you do this, so it is very important to put a bucket underneath the filter to catch the liquid. You will then want to remove the fuel lines and the filter. 


To clean the filter you will want to pour out the excess gas and then clean the filter with a pressurized carburetor cleaner. Make sure to dry the filter out before you reinstall it. 


If you want to have the work done at an autobody shop, it should cost you anywhere from $63 to $165. If you want to have the filter replaced entirely, it should only cost an additional $60 or so. The filters should be replaced about once a year.

A Vacuum Leak

A vacuum leak occurs when there is a leak between the engine and the car’s mass airflow sensor. This sensor is most often located near the air filter box. When you have a vacuum leak in your car, the check engine light will come on and the car may begin to rough idle, there may even be a hissing noise coming from the car. 


A problem with the vacuum system can be rather hard to determine because the engine may run just fine if the car is traveling at a high speed but it will run rough at a low speed. When this happens, your car is likely to stall out when you stop at traffic lights. 


It costs anywhere between $88 and $111 to get a leaking vacuum replaced by a mechanic. 


Where to go for Repairs

Most consumers greatly prefer to go to an independent autobody shop for repairs. A private shop will charge less than a dealership and you will be able to have a one on one consultation with the mechanic. AAA offers a list of approved mechanics and you should be able to find one in your area.


An auto dealership will charge you almost twice as much as an auto body shop and they will charge you buy the job and not the hour. However, they will be experts when it comes to your particular type of automobile. 

Your best option is to find an auto body shop with a mechanic who is certified in your particular make and model of car. 


If you take your car to a mechanic and you find that it would be more expensive to repair it than it would be to replace it, you may want to sell your car and get a new one.

Sell Your Vehicle to Cash Cars Buyers

Cash Car Buyers will give you a great price for your used car. All you have to do is fill out our simple online form and answer a few basic facts about the vehicle. Someone will call you right back and make you an offer. if you accept the offer, we will make an appointment to come and get your vehicle. 


When our employee arrives, they will perform a quick inspection, pay you in cash and tow away the car for free, nothing could be simpler, so fill out our form today. 

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