Symptoms, Causes, and Fixes of Oil in the throttle body

Your car’s air intake system comprises different components that help regulate the amount of airflow into the engine. One of which is the throttle body. If the throttle body works fine, only clean air should pass through it to the engine to help combustion. 

However, as a car owner, you may notice oil in the throttle body during maintenance. So you may wonder what an air regulating device has to do with oil. This article will explain why there is oil in the throttle body, the symptoms, and possible fixes.

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Oil in throttle body symptoms

Vehicle owners have noticed oil in their throttle bodies when doing maintenance. But if you’re not touching your car, how else can you tell there is oil in the throttle body? It’s simple, look out for these oil in throttle body symptoms.

Rough idling

The throttle body supplies the right amount of air needed for engine combustion. However, when there is oil, dust, or other contaminants, this function is interrupted, leading to an insufficient air supply to the engine. Because the engine does not get enough air, proper combustion will not take place. This leads to rough engine idle.

While an oily throttle body could cause the rough engine idle, other components are still responsible for it. So a good way to know an oily throttle body is responsible for rough idling is if you notice low idle during start-up or interruptions when coming to a stop. Another way to figure out an oily throttle body is if your car keeps jerking up and down while producing strange noises.

Uneven or slow acceleration

Throttle bodies in modern cars utilize sensors that help detect the amount of air flowing into the engine. These sensors, in turn, send this data to the engine’s computer, which it uses to regulate the fuel injectors in each cylinder. Ensuring the fuel entering the engine is proportional to the air entering the engine.

So basically, the throttle body also helps regulate the engine’s air-fuel mixture. However, when there is oil in the throttle body, it interferes with this function, so the engine won’t get the right amount of air-fuel mixture needed for combustion. Hence, not allowing proper combustion and invariably makes acceleration challenging.

However, other issues can also be responsible for hard acceleration. So how do you detect oil in the throttle body is responsible for it? Your car accelerates unevenly when you step on the accelerator pedal. For example, the car can be unusually faster sometimes and, other times, slow down unexpectedly.

Smoky exhaust

Should there be oil in the throttle body? No. Even little oil in the throttle body will usually restrict airflow and cause issues such as rough idling, hard acceleration, etc. However, when you have lots of oil in the throttle body, it’s different. Oil can enter the combustion chamber and burn with your air-fuel mixture. Hence, leads to the emission of excess white smoke from the exhaust.


When there is oil in the throttle body, airflow is disrupted, so you won’t get enough air in the combustion chamber. Insufficient air in the combustion chamber often leads to incomplete combustion. When incomplete combustion takes place, your engine will start misfiring. However, this might not always be the case, as dirty spark plugs and other ignition components can cause engine misfires.

Illumination of the check engine light

Many vehicles come with an electronic throttle control (ETC) which helps to keep track of throttle body performance. Just like other car components, when the ETC senses the throttle body isn’t functioning, as usual, it sends a signal through your check engine light.

However, many other faulty components can trigger this light. So while illumination of the check engine light doesn’t necessarily point to an oil throttle body, you will at least know there is an issue.

Increased fuel consumption

If your vehicle uses more fuel than usual, you may want to check the throttle body for oil or other dirt. Since lack of air causes rough idling, hard acceleration, etc., the engine will have to work more than usual.

While your engine will continue running, it will be working harder than usual, leading to high fuel consumption. However, several other factors can be responsible for bad gas mileage.

oil in throttle body symptoms

What causes oil to get into the throttle body?

If you’ve noticed oil in your throttle body or seen some symptoms above, you may be wondering. What causes oil in the throttle body?

Excessive crankcase pressure

The piston ring and valves act as seals to shade away combustion gases. If, however, these rings and valves are faulty, they will allow too many blowby gases into the crankcase. When the crankcase is pressurized, it can forcefully send engine oil onto the breather and then your throttle body.

Again, if the crankcase has too much oil, it will look for ways to release some oil. This exerts pressure on the crankcase, forcing it to release oil into the breather from where it enters the throttle body.

Failing positive crankcase ventilation (PCV) valve

The PCV valve helps to divert blow-by gases, thereby reducing its effect on the crankcase. However, when this valve gets faulty, it allows too much blow by gases which causes excessive pressure in the system. This excess pressure forces engine oil through the system piping into the air intake tube. 

So how does oil get into the throttle body? The inlet tube is connected to the throttle body. So the oil forces its way from the intake tube unto the throttle body and even the intake manifold since both components use the same plumbing.

PCV system failure

The PCV comprises different piping that helps divert blow-by gases from your engine. If any of these pipings gets closed or clogged with sludge, the system may become pressurized. Hence, forcing oil into the air intake chamber. Because the inlet chamber is connected to the intake manifold and throttle body, you will also see oil in the intake manifold and throttle body.

Aging engine

Vehicles have a lifespan to attain, after which they become less active. An engine with so many miles may eventually have its seals and rings weakened. Because these components are weak, they may allow excess blow-by gases to pass through them, forcing oil out of the system. Hence, it results in oil in the intake manifold and throttle body.

Using the wrong piston rings 

Piston rings are found in the combustion chamber and help shield blown gases away from the crankcase. These rings come in two types–cast iron and moly rings. So what ring you use depends on your engine’s capacity.

However, if you use a ring that can’t withstand blow-by gases from your engine, much pressure will be exerted on the crankcase. Thus, forcing the crankcase to push oil into the throttle body.

Ring sealing issues

While rings help to divert blowby gases from the crankcase, it needs to be sealed correctly to do this. If, however, the rings are not properly sealed, it will result in excess pressure on the crankcase, forcing the crankcase to push oil into the throttle body.

oil in throttle body diesel

How to fix oil in the throttle body

First, identify the cause. While we have highlighted some symptoms indicating you have an oily throttle body, making a proper diagnosis would point to the exact cause. You could do a compression test or use a scan reader. That said, here are possible ways to fix an oily throttle body.

  • Replace faulty PCV valves.
  • Ensure all the piping in your PCV system is free from sludge. You can do this by uninstalling and cleaning the blocked pipes.
  • Don’t go beyond the recommended engine miles. If, however, you have already recorded many miles and you don’t intend to change your engine or sell your car, clean the throttle body with a throttle body cleaner. But keep in mind that the situation may arise again since your seals are already weak. Better still, having the engine rebuilt, though, can be costly.
  • Drain out excess oil from the crankcase
  • Change worn-out rings and valves
  • If your rings are not properly sealed, try to fasten them properly. However, you may need the services of an expert mechanic to do this because it is an advanced task.
  • Rings come in different types, so ensure you’re using the rings that can withstand your engine’s blow-by gases. Cast iron rings are cheap, but they break easily and won’t last long. Otherwise, get the moly rings, as they can stay for a long without damage.  
  • Lastly, after fixing whatever is causing the issue, ensure you clean the throttle body with a throttle body cleaner.


Q: What does it mean if there is oil in your throttle body?

Oil in the throttle body, no doubt, is not new among cars. But what does oil in the throttle body mean? It means some failing components need to be repaired. These components are connected to the throttle, so long they aren’t functioning well, you will keep seeing oil in your throttle body.

Q: Is it normal to have oil in the throttle body?

It is not normal to have oil in your throttle body. While little oil on the throttle body won’t blow up your engine, letting oil pile up on it will restrict airflow and cause many car problems. Technically, if you see oil in your throttle body, one or several components connected to your throttle body need to be cleaned or repaired.

Q: Can the throttle body cause transmission problems? 

Yes! The transmission depends on the throttle body to determine the engine power needed. This gets done through the throttle cable connected to the throttle. Ideally, when you press down the gas pedal, you want more power. The throttle cable relates this information to the throttle body, which then supplies the air-fuel mixture needed for combustion.

However, if the throttle body gets blocked by oil or becomes faulty, the engine won’t get enough air-fuel mixture for combustion, limiting the power supply. Because you don’t get enough power, you will experience transmission problems such as rough engine running and challenges shifting gears. And sometimes the engine won’t even start.

Q: What can damage a throttle body?

One of the major causes of a throttle body failure is contamination. Over time, the throttle body can get clogged due to grime or dirt accumulation within the throttle body.  Thus restricting air-fuel flow and invariably limiting engine performance. 

Q: How many hours does it take to replace a throttle body?

With the right knowledge, replacing a throttle body should take only an hour. If you choose to clean, you’re still expecting to spend the same time. 

Q: Can I clean the throttle body myself?

Yes, you can. Just ensure you have the right tools and DIY knowledge. You will need a throttle cleaner, a 4-in-1 screwdriver, a nut driver, compressed air, paper towels, and plastic gloves for safety purposes.

Q: Can I replace the throttle body myself?

Yes, you can. Just ensure you have the knowledge and the right tools. However, if you’re doing it to save a huge cost, that will not happen because most of the replacement cost lies in the cost of the throttle body. While throttle body replacement costs around $250-$650, the throttle body costs around $200-$500, with labor lurking around $50-$150.

Q: Can a dirty throttle body cause shifting problems?

A dirty throttle body will restrict airflow. And because the engine does not get enough air for proper combustion, you will not get enough power to shift when you hit the gas pedal. So yes, a dirty throttle body can cause shifting problems.

Final Words

Oil in the throttle body indicates that certain components connected to it need to be cleaned or repaired. Ignoring an oily throttle body could mean problems for your engine. Consequently, this may result in rough idling, increased fuel consumption, shifting problems, etc. Worse is if the oil gets too much in the throttle body and makes its way into your combustion chamber.

Aside from the problem that can arise, the issue causing the oil, if not attended to, may also affect other related car components. So if you suspect there is oil in your throttle body, carry out a proper diagnosis immediately and fix the leading cause.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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