Did your car used to idle significantly better than it is now? Do you start the car in the morning and the RPMs do a dance before the car finally settles down? The car might even stall if you don’t put your foot on the gas for a few seconds.
There are a variety of causes that could be leading to an annoying idle. Luckily, many of them are extremely easy fixes that any car owner, no matter how unskilled at turning wrenches, can fix.
In this article I’m going to discuss a bunch of easy fixes that you can perform at home to get your car’s idle right. At the end I’m also going to discuss some of the more mechanically involved repairs that sometimes are the culprits.
I bought a 1994 Ford Ranger two years ago that ran like absolute dog sh@@. The coolant gauge went up and down sporadically and the idle was so bad anybody else looking at the truck would think it’s next stop was a junkyard. I bought it anyway, applied these tips and the idle smoothed right out! Of course that did not fix my coolant problem, which was significantly more involved, but it fixed the idle!
Replacing the air filter is basic maintenance, takes ten seconds, and costs about $10. Your air filter is an extremely important, if often overlooked component. Most air filters make use of a folded paper component, and they become clogged overtime. Really old ones are often packed with dead bugs, dirt, leaves, etc.
A clogged air filter will disrupt the flow of air to the engine and will cause a rough idle.
When you replace the old air filter make sure that you clean out any crap inside of the filter box. Leaves and dead bugs will often accumulate at the bottom of the air box.
Spray MAF Sensor
A long time-ago cars had carburetors, which had to be tuned and cleaned out every year for them to run right. Luckily we live in the 21st century and modern cars need significantly less cleaning, but parts still get gunked up over time.
One of the most common parts, which is also extremely accessible is the mass air flow meter. This bad boy is located between the air filter and the intake manifold, making it extremely accessible.
WARNING: Always use mass air flow sensor cleaner for cleaning this sensor. Do not use any other type of cleaner. This sensor is extremely sensitive and you are going to need to be careful with it.
- Remove the sensor. Usually you don’t need to remove the airbox, the sensor is usually screwed into the mass air flow housing with two or three screws. Most of the time they are regular Phillip’s heads.
- If the sensor has not been cleaned or replaced in a long time you should notice a lot of gunk on the sensor itself. Spray it liberally with the Mass Air Flow Sensor Cleaner.
- Let the sensor dry for twenty minutes before re-installation.
This is slightly more involved but should take no more than twenty minutes. The first thing you should do is go pick up some throttle body cleaner and have some paper towels handy.
The throttle is easily accessible on any car. It is located between the mass air flow meter and the intake manifold. It will be bolted directly onto the intake manifold, and it is connected to your gas pedal with a linkage cable. Most throttle bodies are made of aluminum.
You would be surprised at how much gunk that throttle body butterfly valve collects overtime. Sometimes it collects enough to the point where the valve has difficulty opening and this will cause a rough idle or even your car to stall.
WARNING: When cleaning the throttle body it should be performed on a
- Remove the air filter box and mass air flow sensor. The air filter box is usually fastened to the mass air flow meter with some type of hose clamps. I usually disconnect these with my fingers, but depending on the car you may need a flathead screwdriver.
- Remove the rubber hose connected to the throttle body. Usually this is connected with a hose clamp that you can remove with a Phillip’s or flathead.
- Depending on the type of throttle body you have it may have two butterfly valves or it may just have one. This makes no difference except you clean both valves if it has two.
- Open the throttle body valve, spray with throttle body cleaner and clean out the gunk with a paper towel.
- Wait twenty minutes and then put everything back together.
Idle Control Valve
The idle control valve’s job is to regulate the car’s idle based on how much air gets into the engine. The idle control valve can fail in two ways: it can be a mechanical problem where the valve gets stuck from carb buildup; or the sensor component can fail. Cleaning the idle control valve will not fix the sensor, but it will fix a stuck valve.
The idle control valve varies in location depending on the vehicle. For most vehicles it is located on the side of the intake and you do not need to remove anything except the valve. For some vehicle however, like BMW, the idle control valve is located underneath the intake and requires.
Pop the hood and check where the valve is on your vehicle. It will usually be mounted onto the intake manifold and in plain view. Idle control valves vary by car in terms of size and appearance so check what your model vehicle should look like.
You will need to remove the idle control valve to clean it. Spray the valve liberally with throttle body cleaner and then wait twenty minutes to put everything back together.
The fuel filter is on this list because it usually costs under $15 and it takes less than twenty minutes to replace. Although, you will need a jack and jack stands for replacing the fuel filter, it is an extremely quick job.
WARNING: You need to relieve the pressure on the fuel lines before you replace the fuel filter. Trust me, the last thing you want today is to take a gasoline bath and go to sleep for the next few nights smelling like a fuel tank (been there, done that).
Tools you will need:
Eye protection, gloves, fuse puller, jack, jack stands (or wooden blocks), and whatever tool your vehicle requires to remove the fuel filter.
- Relieve the pressure on the fuel line. Check your fuse box, pull the fuse labeled “fuel pump”, cut the engine on and wait for it to die.
- Jack the car up and put whatever side that the fuel filter is on on jack stands. The vast majority of the time the filter will be underneath the car, but it might be on the driver or passenger side.
- The filter might be attached to the hoses with clamps, threaded fittings, or quick-connect fittings. Some just require a screwdriver and others require a special tool.
- Fuel Filters often have to be installed in a certain direction, check if there is an arrow on the fuel filter. The arrow indicates the direction of the fuel.
- Re-install the fuse and start the car!
NOTE: The fuel system will have to pressurize and you will likely have to start it a few times.
Spark plugs are cheap, usually running under $5 a piece and they are usually easily replaced. I say usually easily replaced because some vehicles make it a pain in the a$$ and require that you remove the intake manifold. Check your model car to see how easy it is to replace your plugs.
Spark plugs are responsible for delivering the electric current from the ignition system to the combustion chamber to ignite the compressed air/fuel mixture.
Spark plugs need replacement at certain intervals. Failure to replace spark plugs will eventually be a source of a rough idle. Spark plugs can eventually be fouled by carbon deposits or oil. Spark plug electrodes also wear out eventually and will cause too big of a gap.
Depending on the age of your car you may have spark plug wires or ignition coils. Spark plug wires can be regularly replaced with spark plug wires, ignition coils are less frequently replaced and significantly more expensive.
- Remove the spark plug wire or ignition coil. Spark plug wires are usually just pulled off from the plug whereas coils are usually held down by a clamp and/or a bolt.
- You will need a spark plug socket to remove the plugs, go to your local autostore and ask for one, they are only a couple of bucks and they are extremely useful. Depending on the engine you may also need a ratchet extension and/or swivels to get to all of the plugs.
- Most spark plugs are pre-gapped by the manufacturer but it’s never a bad idea to buy a $1 gap tool and double-check that they are properly gapped to your vehicle’s specifications.
- After checking the gap I usually dab a little anti-seize onto the spark plug threads. I have seen spark plugs seized onto an engine head and it can quickly turn into a nightmare. When re-installing check the torque specification for your vehicle. Spark plugs never require significant elbow grease.
- Once you have installed the plugs, re-install everything and start the vehicle!
Fuel injectors have tiny pin-prick holes on the end of the nozzle which can get clogged overtime. Unfortunately it does not take much clogging to cause a significant idling problem.
SOMETIMES you can get lucky and throw some fuel injector cleaner in the gas tank. It’s best practice to do this every now and again anyways, but it can help with a slightly clogged injector.
If it does not help you could be looking at a significant bill to fix that idling problem. An individual fuel injector frequently costs around $100, and they often require more involved labor than the scope of this article.
If you suspect your fuel injectors are causing an issue, I highly recommend that you buy a $5 bottle of fuel injector cleaner before you consider the alternative.
Hope this article helped! The good news is that these easy repairs will fix many rough idles and they are all a part of your normal vehicle maintenance anyways.