How do you diagnose a throttle body?

If you’re having a problem with your vehicle and notice that you have poor acceleration, or maybe it just seems a little bit doggy. It doesn’t want to go when you push the acceleration pedal or when your engine is idling, and you happen to notice that your RPM or the engine speed goes up and down, kind of erratic idling; you probably have a lousy throttle body. I’m going to show you how to diagnose and fix a car or truck throttle body.

Locate the throttle body: The first thing you want

Locate the throttle body: The first thing you want to do to start the diagnose is to find the throttle body. That said, you have to follow the air filter along the air duct straight to the engine. The throttle body is usually located at the part close to the air intake. As you can tell, not all vehicles are the same. In older vehicles, the throttle bodies are typically integrated with the carburetor.

Remove components blocking access to the throttle body: Remove the air intake duct by loosening the fasteners with a screwdriver and take it out of the way. Then, loosen other components blocking access to the throttle body.

Visually inspect the throttle body: Visually inspect the throttle body by looking out for any dark areas that may look like they have some carbon or debris of any sort. Anything like that could cause the butterfly flap inside the throttle body to restrict somehow, which of course, will cause delayed acceleration when you push down the gas pedal.

Inspect the electrical connectors: Unplug the electrical connectors and inspect inside for corrosion of any sort. Any corrosion between the electrical connectors could cause resistance, and of course, that can cause an issue.

Remove the throttle body from the vehicle: Remove the throttle body from the vehicle: Take the correct socket set and ratchet handle from your mechanic tools box and loosen the bolts holding them.

Clean the Throttle Body: Depending on how clogged the throttle body is, by merely looking at the front, you might think it’s not really in the worst condition, but the flip side might say otherwise. You have to clean all the horrible spots inside. When cleaning a throttle body, don’t use any multi-purpose solvent. You have to make sure you specifically get a throttle body cleaner or make sure it’s written carb and choke. Spray the cleaner inside the throttle body and clean off the dead spot with a light washing brush.

Reinstall The Throttle Body:  Coat the throttle body surface with a slight sealant and fix it back. Tighten the bolts that hold it in place and fix everything you remove early. For visual clarification, watch this video.


Can You Drive With A Bad Throttle Position Sensor?

Technically you can still drive with a bad throttle position sensor. However, do note that a bad throttle position sensor can cause inability to shift up, rough or slow idle and lack of power when accelerating. 

Driving with these symptoms will put you and other drivers around you in danger, so you should bring your car to a mechanic as soon as possible.

Is it expensive to fix a throttle position sensor?

A throttle sensor is no motor swap but it could still get tricky. Depending on what type of vehicle you have this job could get expensive. If your vehicle has the throttle out in the open in a visible and accessible area then the job shouldn’t be too hard and it could cost you under $500 fix with parts and labor. Now some cars can get complicated as the throttle is inaccessible at first and will require tons of disassembling like taking off the intake manifold and air filter box. The price could easily double and get close to $1000.00 just for one small sensor.

Reduced Fuel Mileage

Due to the disturbed fuel ratios, it’s quite obvious to see a drop in your MPG. Whether the bad TP sensor fluctuates the airflow or creates a wides open throttle, in any case, the engine will be running on an improper mixture and wasting fuel. The poor fuel economy will generally be accompanied by a sluggish engine performance as well due to much of the power will be squandered away.

Here’s How To Replace a Throttle Position Sensor

Let’s get started!

Disconnect the Battery

Before you start work, disconnect the battery’s negative terminal cable. This will prevent unwanted shocks to you and damage to other components under the hood.

Unplug Old Sensor

Once you’ve located the sensor’s position, you should be able to unplug the wiring harness that connects it to the vehicle’s computer system. Carefully unplug it, taking notice of any clips or connectors that need to be moved.

Remove Mounting Screws

Once it’s disconnected, you should be able to remove the screws that hold the sensor in place. Keep track of them in case you need to reuse them to install the new one.

Remove Old Sensor

Pull out the old sensor and dispose of it according to local regulations. 

Mount and Screw In New Sensor

Reversing the process, screw in the new sensor in the spot that the old one was pulled from.

Re-Plug Wiring Harness

Carefully re-plug the wiring harness into the new sensor, taking care to pay attention to clips and connectors that need to be aligned for proper installation.

Reconnect Battery Cables

Reconnect the negative battery terminal. Congrats! The job is done!

What Are The Symptoms and Signs Of a Failing Throttle Position Sensor?

You may not think much about your car’s TPS, but you’ll notice when it starts to go bad.

Lack Of Power

If your engine isn’t getting the fuel it needs, or is getting too much, you’ll notice that it doesn’t seem to be accelerating as it should be. When you put your foot down, the TPS should be screaming out for more fuel, but it won’t if it’s malfunctioning. If the opposite happens, your vehicle may surge forward when you’re not intending to speed up.

Trouble Accelerating

In a similar vein, you may notice that your car will accelerate, but won’t get past a certain speed. It might feel like the car just fizzles out after first or second gear and won’t upshift or go any faster.

Uneven Idle

If your car can’t maintain a constant engine speed when it’s sitting still, your TPS may be on its way out. A constant level of fuel delivery is necessary to maintain a steady idle.

Check Engine Light

On its own, a check engine light can mean absolutely nothing, or can mean something catastrophic is happening. If it’s seen in conjunction with any of the symptoms above, it’s a good indicator of TPS issues.

You might see a check engine light when the TPS starts to fail., Depositphotos

How do you test a throttle position sensor?

Testing a throttle position sensor requires either an ohmmeter or a voltmeter. If you have a multimeter, then this works too since that includes both tools. You need to test the resistance across the sensor with the accelerator pedal in different positions. Verify the readings against the specs in a repair manual. If the readings are outside the specs, then the sensor is bad.

3. Car accelerates, but won’t exceed a relatively low speed, or shift up

This is another failure mode of the TPS, which indicates that it is falsely limiting the power being requested with your accelerator pedal foot. You may find that your car will accelerate, but not beyond a speed of 20 – 30 MPH. This symptom often goes hand in hand with loss-of-power behavior.

What Happens If Your Throttle Position Sensor Is Faulty?

There are many reasons behind a bad throttle position sensor and there are many signs of a bad TPS. When it happens, it leads to poor fuel economy and moreover puts you and other drivers around you in danger. It can also result in issues when setting base ignition timing, or changing gears.

The TPS can gradually fail or all at once. In most situations, when the TPS is broken, the Check Engine Light will turn on to warn you about the issues. Additionally, most carmakers supply a “limp home” mode of operation with decreased power if there is a failure in your engine. This is made to enable a driver to get off a crowded highway in a safer way.

And when you detect there is a problem with your TPS, everything you need to do is to replace it immediately. When replacing the TPS, you have to clear related fault codes and may need to reprogram the software of the new TPS module to fit with other engine management softwares. The best way is bringing your car to a skilled mechanic who can inspect and install the right replacement part.

How To Fix A Bad Throttle Position Sensor

Most of the time, a bad sensor cannot be fixed. You will need to replace the TPS with a new sensor. You will, however, need to diagnose the problem before replacing the sensor. You want to make sure that the TPS is the root cause of your issue so that you don’t replace it for no reason.

Testing a TPS is not difficult, but it does require some special tools. Depending on your vehicle’s type of sensor, you will need either a voltmeter or an ohmmeter. If your vehicle has a potentiometer sensor, then you will use the voltmeter or multimeter. If it has a switch and combination TPS, then the ohmmeter is what you will need.

You should record the resistance of the TPS while pressing the accelerator pedal. A repair manual should list acceptable ranges for the resistance at various throttle positions. If the readings you get are outside these ranges, then the sensor is bad and will need to be replaced.

Replacing the sensor requires disconnecting the electrical connector and removing a few screws in most cases. The only issue that you might run into is the fact that the TPS can be difficult to access on some vehicles. It might require removing other parts first so that you can get to the connector and screws holding the TPS in place.

What Does a Throttle Position Sensor Do?

A throttle position sensor is similar to the motor cortex in the human brain, it controls one of the most important components of the car that keeps your engine running like a throttle body. Picture a little module in the car that reads how far down you have pressed the gas pedal. It gathers that information and relates it to the mass airflow sensor and the engine’s RPM to make sure that the correct amount of air/fuel ratio is going into your engine properly.

What is a throttle body?

Mass Airflow SensorAn engine needs two things to stay running which is air and fuel. Normally a car will pick up air through the intake and passes it through the Mass Airflow Sensor. The air will travel up the intake and it will reach your throttle body. The throttle body is a circular valve that’s located in between your air filter and Intake Manifold. In the old days, there was a wire attached to the gas pedal of your car and it would move accordingly to how you pressed it. Nowadays there is an electric system that’s far more efficient than the old ways but it can still have issues.

What happens when my throttle position sensor goes bad

When a TPS goes bad, then the car’s throttle body won’t function properly. It could either stay shut or it won’t close properly which is a severe issue. If it stays shut then your engine is not going receive air and it won’t start. When the throttle gets stuck in an open position than your vehicle will receive too much air and cause it to have a high or fluctuating idle.

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