One way to describe an internal combustion engine is to think of it as a big air pump. It sucks in air, adds fuel, compresses and ignites the mixture, then pushes the air out the exhaust.
The main thing controlling the speed and power of the engine operation is how much air is allowed in. The component that controls how much air enters the engine is the throttle body, which is a cylinder with a rotating plate that opens or closes on commands from the gas pedal.
On older vehicles, the throttle body is operated by a cable, but most throttle bodies on modern engines are operated electrically. A sensor on the gas pedal is read by the PCM, which tells the motor on the throttle body plate how far to open.
The throttle body usually bolts directly to the engine’s intake manifold. An air intake tube leads from the throttle body to the air filter housing to provide air intake.
On most engines, the throttle body is on the top of the engine or otherwise easily accessible, though there are a few where the intake angles down and away, rendering replacement a little more difficult. Some turbocharged engines also have more complicated air intake systems and more in the way of accessing the throttle body.
Throttle Body Replacement Costs
Some estimates of the throttle body repair cost on some common vehicles using £70 to £100 an hour as a labour rate and assuming that book time is used are presented below:
- For a 2006 Ford F-150 with a 5.4-liter engine, the labour time is estimated at 0.7 of an hour. A factory throttle body costs about £375, and a non-factory replacement part costs about £155. The total job cost is around £425 using OE parts and about £200 using aftermarket parts.
- For a 2005 Jeep Liberty with a 3.7-liter engine, the labour time is estimated at 0.6 of an hour. A factory throttle body costs around £403, and an aftermarket replacement part costs about £200. The total job cost is around £445 using factory parts and about £242 using aftermarket parts.
- For a 2009 Volkswagen Jetta with a 2.0-liter engine, the labour time is estimated at 1.4 hours. A factory throttle body costs about £450, and a local replacement part costs about £185. The total job cost is around £550 using OE parts and about £280 using aftermarket parts.
- For a 2004 Toyota Corolla with a 1.8-liter engine, the labour time is estimated at 1.5 hours. A factory throttle body costs about £670, and a non-OE replacement part costs about £220. The total job cost is around £775 using OE parts and about £325 using aftermarket parts.
Very rarely does a throttle body have an obvious failure where other things can be easily ruled out. Most of the time, a flat one-hour diagnostic charge will be added.
There are engine self-diagnostics that can set an engine light and a trouble code that points directly to a throttle body failure. However, even in these cases, there are other possible causes that should be ruled out during diagnostic checks before replacing a throttle body.
One of the best ways to save money on throttle body replacement is to be very sure that the part actually needs to be replaced.
Other Things That Might be Recommended
One of the common ways that a throttle body can cause problems is if the throttle plate becomes gummed up. All the air entering the engine goes past the throttle plate, and a certain number of deposits on and around the plate are inevitable.
Very often, depending on the symptoms, cleaning of the throttle body will be recommended before or during the diagnostic process. This can be done manually or it can be done with a chemical spray injected into the running engine to clean the entire intake system.
Usually, it is an additional charge and is recommended as a maintenance service if needed prior to other work being done.
Many throttle body codes are related to flow issues where the PCM commands a certain throttle plate opening. However, it doesn’t see the corresponding vacuum or airflow changes that it expected to see.
There are several different operating strategies depending on the vehicle and engine. But if a sensor in the system gives an inaccurate or sluggish reading, that can look like a throttle body problem.
Part of the diagnosis, sometimes, is to check and verify various sensors. It happens sometimes that a sensor can test as faulty, and then, it will usually have to be replaced before further diagnosis on the problem can be made.
Ideally, when something goes wrong, it is only about one thing. However, sometimes repairs are complicated. On a throttle body issue, the best initial decision is to find a mechanic who is experienced and comfortable with the job.