What are the Symptoms of a Bad Throttle Body & How Do You Fix It?

In this article we will be looking at an important part of the fuel to air ratio, the throttle body. We will learn more about this part such as what it does, how you can recognize that it is broken and of course how much replacing such a part might cost you.

Why Is the Fuel/Air Ratio Important?

We will start this article with a little bit on the importance of good fuel to air ratios. Generally speaking the ideal ratio is 15 parts air to 1 part fuel or 15:1. This mixture of air and fuel gets released into the numerous cylinders of the internal combustion engine, compressed and then ignited with a spark.

The cylinders in the engine will ignite in a pre-set sequence over and over to help create the rotation of the engine. The rotation of the engine is then transferred by a series of shafts to the drive wheels and of course makes the car move.

The speed of the car and other conditions are often factored into the fuel/air mixture and many modern vehicles have complex sensor set ups to create the most efficient conditions for the engine. When these fuel/ air mixtures are off this can cause problems.

A mixture with too much fuel is known as being rich and often results in unburned fuel remaining in the cylinder. This is not good for the engine and is definitely not good for your fuel economy.

A mixture too heavy on air is known as lean and this can result in a weak combustion event which is known as a misfire. These misfires are also very bad for the engine over time so they should be fixed.

What Is the Throttle Body?

So now we come to the part in question, the throttle body. As mentioned this part of our engine has a role to play with the fuel/air mixture. It is basically a butterfly valve that helps control the amount of air entering the engine. It is specific however to fuel injected vehicles.

If it lets in too much we get lean conditions in the cylinders, but not enough and we can end up with a rich fuel/air mixture. This valve then opens according to the pressure applied to the accelerator allowing in more air as you press down.

At the same time more fuel will enter the system and the cylinder combustions will become more frequent allowing the car to accelerate. When we relax the pressure on the accelerator then the valve closes letting less air in and then the engine slows accordingly.

Most vehicles only have one throttle body but some larger ones may have more depending on the engine's needs.

Indications of a Throttle Body Issue

Many of the symptoms of a failing throttle body can be attributed to other issues as well so this part may be just one of a few things you will check. There are several things that can indicate an issue with the throttle body however so it is good to know what to look for.

Check Engine Light

Generally speaking the check engine dashboard light is going to be your first indication that you have some form of issue developing. It is however a universal warning light that can mean potentially hundreds of different faults.

The light alone then will not tell you that the throttle body is the issue although the error code recorded in your vehicle's electronic control module (ECM) will tell you. Using an OBD2 scanner tool you can plug into your car's ECM and get a reading on the recorded error codes.

If you check your owner's manual for a list of error codes you can use the data from the scanner to determine what issue was detected. This may very quickly alert you to a throttle body issue and this is something you should fix right away before other issues arise.

Rough Idling

You may have been driving your car for years so you might notice if it sounds odd during idling or has any strange vibrations that it lacked before. If the idling jumps up and down this may be an indication of a damaged throttle body.

This is going to be most notable while idling as the vehicle is at its most sensitive. Things may not feel different while traveling at speed so take note of how your car reacts while idling.

You may also notice that your RPMs are high while idling. This may mean that the throttle body needs to be recalibrated which is also something you can do with a quality diagnostic scanner.

Stalling while at idle can also be an indication that the throttle body is starving the engine of air. Your RPMs will be low when idling and eventually the engine will just stall. This should not happen while idling so it is likely a throttle body issue.

Rough Acceleration

As mentioned while you are at a stable speed you may not notice new sounds or vibrations but rough acceleration can be very telling. While we accelerate the throttle body should be working to help maintain that fuel/air mixture.

Uneven acceleration that skips between fast and slow can be an indication that the throttle body may not be doing its job.

Misfires

We already mentioned the term misfire earlier and just to recap this indicates that there is more air in the cylinders than there should be. This causes a misfire which is essentially an incomplete combustion event.

When you rev the engine you might notice small bumping sounds coming from the engine bay. This will be the sound of a poor cylinder combustion and this is not good at all.

Engine Performance and Efficiency

A bad throttle body can have an impact on your engine power meaning you might notice that the vehicle has not quite got the acceleration it usually does. Sluggish acceleration indicates that the system is not getting enough air.

Another symptom of too little air getting to the engine can be rich fuel/mixtures. This means more fuel is being used than normal and may make an impact on your fuel consumption. If you are filling up more often but not driving more then this may indicate a throttle body issue.

How Much Does a Throttle Body Replacement Cost?

This is by no means a cheap part to replace with a new unit averaging between $200 - $500 without factoring in labor costs. Depending on the car the cost of labor for this replacement ranges from $50 - $150.

This all means that throttle body replacement alone can cost somewhere between $250 - $650 without factoring in any other repairs that may be needed. If you catch the problem early then hopefully nothing else will need fixing. Not getting the problem fixed quickly enough may damage other parts of the engine and really increase your costs to get back on the road.

Where Is The Throttle Body?

The throttle body is not one of those parts that is hard to find because thankfully it needs to have a clear path to allow air to flow through. Generally speaking it will be found on the intake manifold at the big hose coming from the turbocharger or air filter.

Can You Do This Replacement Yourself?

In truth this is generally not considered a complicated replacement so if you have some basic mechanical knowledge you may be able to save on the labor costs. There are some models however that need specialized equipment to allow you to reset the throttle body.

Conclusion

It is hard to miss the symptoms of a faulty throttle body but they can also be attributed to a number of other issues as well. When it comes to diagnosing a throttle body problem a simple scanner tool can be your best friend.

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