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 accessed, 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 $100 an hour as a labor rate and assuming that book time is used are presented below:
- For a 2006 Ford F-150 with a 5.4-liter engine, the labor time is estimated at 0.7 of an hour. A factory throttle body costs about $435 and a Standard replacement part costs about $179. The total job cost is around $505 using OE parts and about $249 using aftermarket parts.
- For a 2005 Jeep Liberty with a 3.7-liter engine, the labor time is estimated at 0.6 of an hour. A factory throttle body price is around $464 and an Echlin replacement part costs about $232. The total job cost is around $524 using factory parts and about $292 using aftermarket parts.
- For a 2009 Volkswagen Jetta with a 2.0-liter engine, the labor time is estimated at 1.4 hours. A factory throttle body costs about $519 and a Beck/Arnley replacement part costs about $215. The total job cost is around $659 using OE parts and about $355 using aftermarket parts.
- For a 2004 Toyota Corolla with a 1.8-liter engine, the labor time is estimated at 1.5 hours. A factory throttle body costs about $776 and an Aisin replacement part costs about $254. The total job cost is around $926 using OE parts and about $404 using aftermarket parts.
Very seldom 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 additional.
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 cost-saving approaches to 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 amount of deposits on and around the plate are inevitable.
Very often, depending on the symptom, 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 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 expects to see.
There are several different operating strategies, depending on 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 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.
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 that is experienced and comfortable with the job.