Cars have come very far from the days of carburetors. Nowadays, they use sensors and electronic circuits to ensure perfect air to fuel ratios. The result is more efficient combustion that gives you a cleaner and more powerful engine.
One of the most important components in a modern petrol/gasoline engine intake system is the throttle body.
What is a Throttle Body?
Your throttle body is a tube (often metallic) with a pivoting flat valve referred to as a butterfly. The throttle body controls the flow of air into the engine by varying the size of passage in the intake tube before the intake manifold.
If you have an electronic fuel injection car, the throttle body gets its instructions depending on the accelerator pedal position sensor. The more you depress the accelerator the further the butterfly valve opens hence letting more air into the system.
To ensure perfect combustion, the ECU uses data from the throttle position sensor, the mass airflow sensor, and your upstream oxygen sensor to adjust fuel injection accordingly.
Where is the Throttle Body Located in My Car?
ProTip: If your car has a carburetor (most old engines do) then your throttle body is part of the carburetor. It’s a mechanical component that uses an engine vacuum and a physical cable from the accelerator pedal to control air intake.
Fuel-injected cars have the throttle body sitting between the car’s air filter and the intake manifold. The exact location of this component varies from design to design.
You will, however, note that it will be a chunky metallic construct in the otherwise plastic and rubber intake hose construction.
The throttle body is then connected to your accelerator pedal via a cable or an electronic wire that runs a signal if your car is throttle by wire.
What Are the Symptoms of a Bad or Failing Throttle Body?
While your throttle body should last for your car’s lifetime, it can go bad over time. This is common in high mileage cars that are way beyond their warranty bracket.
Here are the top symptoms that hint at a failed or failing throttle body.
Poor or High Idle
One of the easy to notice symptoms of a faulty throttle body is poor and very low idle. Your car will either idle at lower than specified RPM (you can find this in your manual or on a sticker under the hood), vibrate, or even stall when on idle with a load.
Your engine will also surge or stall if you press the throttle pedal quickly. This happens because the throttle body won’t react to the fast position changes as quickly as it should. If it doesn’t lag, you will notice some inconsistencies or a lag between your input and the throttle reaction.
Your Car Accelerates Slowly and Unevenly
Since a faulty or dirty throttle body doesn’t let in more air when you demand it by pressing the throttle, chances are your car will accelerate slower. It won’t be as punchy and powerful as it used to be.
Sometimes, the throttle body might react in an uneven burst leading to slight or bid noticeable jerks in power delivery. This will make it hard to predict how much acceleration you get with a specific throttle position.
Jerks when accelerating could also mean you have issues with your gearbox or the torque converter if your vehicle has one.
Your car will also seem to drop power or rev up more when cruising even without changing your throttle application or changing the grade you’re driving on.
The Check Engine Light Pops Up
Since your throttle body has a sensor, chances are it will throw up an error code when the performance dips below the acceptable tolerances. Apart from a specific error, you could get other fuel-air mix related error codes as the throttle body position throws off your fuel injector settings.
You could get anything from a rich air to fuel mixture level to a misfire error code depending on the severity of the problem.
Since you will have to disassemble the throttle body before addressing any of these codes, it would be wise to have it inspected and cleaned just in case it is the problem.
Terrible Fuel Economy
Your car could burn more fuel than normal with a bad throttle body. Its errand position throws off the perfect dance your ECU dances to calculate how much fuel it injects into the engine for perfect combustion.
A faulty throttle body could also affect your emissions. You will fail a smog test and if it persists, you could end up ruining your catalytic converter.
Dirt and Grime on the Throttle Body
The most common cause of problems in your throttle body is dirt and grime. Even though the air flowing through is filtered, there’s still some blowback of carbon especially if your engine recirculates exhaust gases.
Over time, dirt and grime accumulate over the butterfly valve in a process called coking. The surface becomes rough making it a bit harder for air to flow through smoothly.
The inside of the throttle body also cokes more since when you switch off the engine, some of the exhaust gases and uncombusted fuel float to the top of the engine. The vapor flows back through the manifold until it encounters the inner side of the throttle body creating deposits.
Dirt and grime accumulates on the outside
Carbon from the engine accumulates on the inside side of the throttle body
How to Fix a Faulty Throttle Body
In most cases, the problems in your throttle body will either be due to dirt or a faulty throttle position sensor. The throttle body itself rarely goes bad. And if it does, you will have to replace the entire thing.
How to Clean a Dirty Throttle Body
Before cleaning the throttle body, you have to get it out of the intake hose assembly. The process varies depending on your engine’s layout. However, most throttle bodies will come out with a set of screwdrivers and some spanners.
Once you identify it, open all the necessary bolts and nuts to free it from the hoses. Remember to note any connectors or hoses you take off and where they go.
It should be easy if you’ve worked on a car before. If it is your first time, consider getting a step-by-step guide specific to your car. Chances are you’ll find it in your user manual.
What You Need to Clean a Throttle Body
To clean your throttle body perfectly, you will need the following
- An air compressor or a can of compressed air
- Some paper towels
- Throttle body cleaner
What to Do
- Spray some air onto the inside and outside of the throttle body to get rid of loose carbon and gunk
- Spray some of the throttle body cleaners to the outside of the butterfly place and use your paper towels to wipe it clean. Repeat until the plate and its surrounding is clean and shiny
- Repeat the same procedure with the inside of the throttle body
- Use your air compressor or compressed air again to blow and dry off all the throttle body cleaner. Alternatively, you can let it sit for a couple of hours and dry off naturally
Reinstall the throttle body and reattach all the cables and hoses.
How to Test a Throttle Position Sensor (TPS)
A throttle body sensor detects how wide open the butterfly on your throttle body is. It could be a potentiometer that sends position as a resistance value or contact points that activate different circuits as the throttle body position changes.
If this sensor is faulty, your ECU cannot tell where your throttle body is. As such, it can’t calculate how much fuel your car needs to run efficiently. Technically, your throttle body will be faulty.
The simplest and most common way to test your TPS sensor is by checking if its resistance varies or voltage changes as the throttle plate position varies.
Here are some troubleshooting steps to follow when testing your TPS sensor.
Check if the Sensor Terminals are Clean and Connected
A lot of things can go wrong if your sensor doesn’t make perfect contact with its terminals. Look for loose and dirty connectors. A loose or disconnected connector means a simple fix.
Also, if you find some dirt, clean it off. Disconnect the sensor and clean its terminals well.
Confirm it Has a Solid Ground Connection
You will need a digital multimeter for this test.
- Set your multimeter to 20V DC
- Turn the ignition to ON but don’t start your engine
- Attach the red lead of the meter to the positive terminal of your battery
- Touch the negative test lead of the meter to each of the three terminals of the TPS sensor
The ground terminal will read 12V. You can note its color for future reference.
If no terminal reads 12V, then you have a ground problem.
Testing Connection to Reference Voltage
Apart from the ground, your TPS sensor also needs reference voltage to work. Testing for this is trial and error unless you know the pinout to your car’s sensor.
- Turn the car to ON but don’t crank the engine
- Connect the red test lead on the multimeter to one terminal (ground) and connect the black lead to each of the other two sensor terminals in turn
- One of the remaining two terminals should give you a 5V reference voltage. You can switch around the red lead to other terminals in case you don’t get the 5V, chances are you are not on the ground terminal
- If you don’t get a 5V reference after multiple checks, the sensor is either faulty or you have some problem in your wiring and aren’t getting reference voltage
Probing for Signal Voltage
Don’t remove insulation to any wires. You can back probe to get access to contactors in the throttle body terminal. By now, you should have identified the ground, signal, and reference wire on your sensor.
- Connect the red test lead of your multimeter to the signal wire and the black test lead to the sensor connector’s ground
- Turn the ignition key to ON
- Make sure the throttle plate is fully closed (no foot on the accelerator pedal and you can inspect visually
- Your multimeter should read between 0.2 and 1.5 Volts depending on your car. Setting the multimeter to 10V DC or lower could help you pick this out. continue to the next step even if you get a 0V reading
- Gradually open the throttle plate while watching the meter readout (have someone step on the throttle pedal gradually)
The voltage on the multimeter should rise gradually and peak out at around 5V when the plate is fully open
The voltage change should be smooth and relative to the rate at which the plate opens
Any spikes or stuck readings means there is a problem with the sensor
If the voltage spikes when you lightly tap the position sensor, then it has a problem. It will give spikes when the car jolts as you drive. You need it replaced
ProTip: some old car models have adjustable throttle position sensors. If yours has one, consider adjusting it first before getting a replacement.
Common Throttle Position Sensor Error Codes
In most modern cars, the ECU will throw a check engine light if it detects a malfunction on your throttle position sensor. This makes troubleshooting easier since the error code from your ECU already tells you what the problem could be.
Here are the most common error codes and what they might mean
| DTC | Description | Potential Fault |
| P0121 | TPS signal disagrees with MAP signal | Faulty vehicle speed sensor signal |
| Bad TP sensor. | ||
| Faulty MAP sensor. | ||
| P0122 | TPS low voltage | Internal short to ground. |
| Sensor or circuit open. | ||
| Sensor or circuit shorted to ground. | ||
| P0123 | TPS high voltage | Circuit shorted to voltage. |
| Sensor shorted to 5V reference voltage. | ||
| Sensor ground open. |