Car Repair and Maintenance

Symptoms of a Bad Throttle Body (& Replacement Cost)

symptoms of a bad throttle body

You need to know the symptoms of a bad throttle body while you keep your eyes on the road and your foot down, it’s the mantra of your favorite ‘Need for Speed’ motor racing video game.

It simply translates thus; press the gas pedal down to accelerate faster.

A throttle body is a tube-shaped housing that contains a flat valve (butterfly) located between the air intake filter (air cleaner) and the intake manifold of the engine.

Its duty is to regulate how much air can go into the engine, depending on how much pressure the driver applies on the gas pedal. It is connected to the gas pedal of your vehicle with a flexible cable or ‘linkage’, which moves the throttle shaft when the gas pedal is depressed.

As more air flows into the engine, it injects more fuel, thus allowing for more power. You may check Wikipedia for a more in-depth explanation of how the throttle body works.

Aluminum is the alloy used to make most throttle bodies. This is part is vital to the smooth operation of your vehicle; so if you want many more years of blissful motoring, you need to keep up with routine maintenance in other to get the best performance out of your vehicle.

The bad news is even with routine maintenance, a machine as complex as an automobile with hundreds of moving parts is bound to develop faults at any time.

Throttle body issues aren’t uncommon in vehicles; they can throw up a wide range of symptoms ranging from minor quirks to major malfunctions.

symptoms of a bad throttle body

Symptoms of a bad throttle body

The good news is you don’t need a Ph.D. in mechanical engineering to diagnose and repair your vehicle, if you’ve got the expertise all you need is a proper set of tools, an instructional manual, a willing heart, listening ears, and capable pair of hands. If you don’t then it’s best you sit this one out and leave it to the experts.

I reckon you get a proper diagnosis of whatever faults you’re having with your vehicle before you start throwing parts at it unnecessarily and it becomes a ‘money pit’.

One of the chief reasons the throttle body throws up problems is coking which occurs due to the accumulation of dirt & grime clogging up the throttle body, creating a rough surface, which disturbs the air-fuel flow and eventually diminishes the efficiency of your vehicle engine.

To be sure your throttle body is the culprit; here are a few symptoms you might notice:

  • Uneven or rough engine idling
  • Engine stalling
  • Poor fuel economy (Mileage)
  • Build-up of dirt inside the throttle body
  • Engine misfires
  • Lethargic acceleration
  • Check engine light coming on
  • Sudden jolts during driving accompanied by complete engine cut-off
  • High RPM idle
  • Electrical Issues
  • Electronic Power Control Light coming on (In the case of Volkswagen group cars; VW, Audi, Skoda, etc.)
  • Airflow disruptions
  • Lack or loss of power

1. Uneven or rough engine idling

This symptom is barely noticeable when it starts out, but in later stages, it becomes more noticeable and intrusive.

When you start the engine, instead of smooth idling it tends to ‘lurch’ and ‘burp’ in an uneven manner as if possessed by a spirit within, when worse the engine might even cut-off completely leaving you worse for it.

2. Engine stalling

At first, you don’t usually see this as being intrusive to your driving experience until it gets worse.

When you press the gas pedal, instead of getting the ‘normal’ instant response as designed, you get a sluggish one, you might feel like there is a delay from the time you press the gas pedal to the time the engine responds to your input when it gets worse it might even feel as if the gas pedal isn’t connected to the throttle body in any way.

On the highway or steep inclines, this can be a potentially dangerous issue to have, so I recommend looking into it immediately before you start seeing this symptom manifesting.

3. Poor fuel economy (mileage)

Remember that the throttle body’s duty is simply to regulate the air-fuel mixture in your engine; poor mileage is simply a result of the faulty operation of this part.

You only notice this mostly when you find yourself having to do more fill-ups than usual for the same distances you normally cover routinely.

This can result in your fuel mileage getting worse by twenty-five percent to as high as fifty-five percent in extreme cases.

4. Build-up of dirt inside the throttle body

Timely inspection is required to notice this symptom on time before it results in something worse, a simple task like cleaning and inspection during an air-filter change may be the difference between a huge issue and the smooth continuous operation of your vehicle.

When the surface of the throttle body gets clogged up with dirt, grime, and filth as opposed to being shiny and clean, the butterfly valve is much more likely to get stuck in an uneven position causing an irregular air-fuel flow and other resultant problems.

5. Engine misfires

This also occurs due to the surface of the throttle body being clogged up with dirt, grime, and filth as opposed to being shiny and clean, the butterfly valve is much more likely to get stuck in an uneven position causing an irregular air-fuel mixture ratio.

Sometimes it feels like a few cylinders in the engine aren’t working at all, the presence of this is usually a sign of a serious problem with your throttle body.

Quick action is needed to tackle this as it can be a potentially hazardous problem on highways or steep inclines.

6. Lethargic acceleration

This is the hesitation between when you press the throttle pedal and when you get a response from the engine, this accompanies all symptoms of a faulty throttle body.

Starts off being barely noticeable but if not nipped in the bud early enough you begin to feel a serious shortage of power and a slower almost lethargic acceleration whenever you press the gas pedal.

7. Check engine light coming on

On modern cars this is usually the first indicator of any problems with the engine, once all of the symptoms of a bad throttle body begin to show up this light would definitely come on.

In minor cases, it may come up and then go off on its own after a few engine cycles, but when the issues get serious it will stay on.

An OBD2 scanner tool is recommended to diagnose the problem whenever this light comes on, or a quick trip to the auto-shop in case you don’t have a scanner handy will save you a lot of headaches, help you avoid any other problems and throw-up any other underlying issues before they start showing up as problems in your vehicle.

8. Sudden hard jolts during driving accompanied by complete engine cut-off

This occurs at the final phase of the problem after you might have failed to address all other previous symptoms of a faulty throttle body.

It begins as a sudden, violent jolt. After which the engine may cut off completely and refuse to start until a few minutes later

This can occur without a moment’s notice whilst driving and any kind of warning.

Early diagnosis and repairs when you notice other symptoms are enough to prevent this kind of symptom from showing up.

9. High RPM idle

This is the first noticeable symptom of a faulty throttle body.

Instead of the engine idling away smoothly, it tends to idle in an uneven manner and most times on higher revs.

It’s almost like the gas pedal presses itself down. Barely noticeable when it starts out but becomes more auspicious as it gets worse.

10. Electrical Issues

A faulty throttle body will throw-up electrical issues in modern cars.

An incorrect air-fuel mixture will throw up wrong data to the car’s engine control unit (E.C.U) thereby causing it to shut down other systems to prevent damage to other parts of the vehicle.

Due to their complex electrical systems, modern cars will switch into “limp mode”; in this mode, the power produced by the car engine is reduced no matter how much you step on the gas pedal.

This feature also helps to prevent further potentially expensive damages to other parts of the vehicle.

Electrical Power Control Light coming on (In the case of Volkswagen group cars; VW, Audi, Skoda, etc).

This is peculiar to vehicles manufactured by the Volkswagen group, other manufacturers may have their acronyms but this is the most common one.

The Electronic Power Control (EPC) light may come on its own or along with the ominous check engine light.

Sometimes it might actually indicate other types of issues but it’s advisable to look at the throttle body first when it comes on.

11. Airflow disruptions

An improperly positioned leaky or stuck butterfly valve can result in an improper air-fuel mixture ratio, which can cause throttle body pressure problems.

When this happens, the engine computer will go into “limp mode” due to the incorrect data its sensors are receiving from the throttle body resulting in various symptoms of a faulty throttle body showing up later on.

12. Lack or loss of power

Related to lethargic acceleration, this is a noticeable symptom when it starts to manifest.

Often occurring during driving; you notice your car feels like it’s ‘bugged down’ because it struggles to accelerate, rev high at idle, or even a complete loss of power on a few vehicle ancillaries such as the air-conditioning or HVAC system.

This symptom usually leads to other issues like terrible fuel mileage and a few others.

Conclusion

In the world of auto parts, price isn’t the only consideration, quality is of the utmost importance, and the reliability of your ‘source’ is also a factor to be considered.

The level of expertise of the ‘hands’ working on your vehicle is another important factor. You may ask around for customer reviews which are a more realistic way of gauging the quality of their work.

Bernard Juchli
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Bernard Juchli

Bernard Juchli is an experienced racer, mechanic and team owner who trusts Avon Tyres. Bernard is the lead driver and force behind his Big Dog Garage Race Team. He is the General Manager and Chief Mechanic of Jay Leno’s Garage. Bernard and his crew of seven are responsible for all repairs, restoration and fabrication of Jay’s incredible automobile and motorcycle collection.

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