People have asked me if they really need a throttle body service. I have touched on this subject in past articles but today I will go a little more in-depth. In my opinion dealership service departments and auto repair centers are recommending this service way too much. When I took my car in for the Cadillac recall the service adviser told me I needed one.
When I got home I removed the air intake hose and shined a flashlight into the throttle body. It was perfectly clean and almost shiny. It most certainly didn’t need a service or cleaning. This isn’t to say a throttle body service is never needed. In fact I do believe they should be done as required.
This means a visual inspection to verify it really is needed. Therefore, if someone recommends this service to you I would ask them, why do I need it. If they tell you, because it’s dirty I would then ask them how they know.
The correct answer to this question is they removed the air intake hose and performed a visual inspection. Or they scanned the vehicle and monitored the IAC (Idle air control motor) steps at base idle. If they didn’t do this I would not purchase the service or at least seek out a second opinion.
What does a Throttle Body Do
The throttle body allows the driver to control the speed of the engine by controlling the amount of air that enters it. The driver pushes on the gas pedal and in the old days the cable would pull on the butterfly inside the throttle body assembly. Nowadays most of these throttle systems are what they call drive by wire.
You can ask Toyota engineers for more details on the system but Basically this means that your gas pedal is now a sensor that sends a signal to the throttle body about how far to open the throttle plate. Each type of throttle assembly is designed to allow a certain amount of air to pass through it with a particular amount of throttle plate opening.
When the throttle plates are completely closed some air is still needed. This is where the idle air control valve or motor comes into play. The IAC valve meters a small amount of air into the intake manifold. The computer controls the idle air control valve and only allows enough air to maintain a steady idle of 650 rpm’s which keeps the engine from stalling. This metering allows the computer to control the idle speed.
The IAC valve can be monitored on an automotive scan tool as mentioned above. How far the valve is opened is counted in steps. The dirtier the throttle the more steps are required by the IAC valve to maintain engine idle.
Therefore you can actually use the steps to diagnose a gummed up throttle body. As an example if you observe on a scan tool that the steps are around 50 this could be considered a little high. After a throttle body service is performed you would most likely see about half of that or below 25 steps.
How to Service the Throttle Body
Modern vehicles are better equipped to compensate for a throttle body that is becoming dirty. So in my opinion the newer your vehicle and the lower your actual mileage, the less likely you need this service. On the flip side of this if you have a 1995 vehicle with 125,000 miles on it and you have never cleaned the throttle body I could just about guarantee that you need a throttle body service.
When carbon and varnish accumulates on the throttle plates or in the throttle bore the amount of air that can pass through into the engine can be reduced. Although this normally causes an idle problem these deposits can be cleaned off of the throttle body assembly and the airflow restored. It is quite possible that you could perform this service on your own in the driveway depending on your skill level.
The carbon deposits can be cleaned with spray type cleaners and wiped off with a cloth. The difficulty of the throttle body service depends on the application. In some cases the throttle body may need to be removed to properly clean the assembly. I use the very complete 3M Diy Fuel System Tune-Up Kitthat comes with a DVD on how to perform the service. It is a three-step kit that includes a fuel additive to be installed in the tank.