DEAR CAR TALK: What the heck is a throttle body?

We have a 2007 Toyota 4Runner with 85,000 miles and a 2011 Toyota Venza with 45,000 miles. Our local Toyota dealer is pushing us to service the “throttle body.”

I agreed to do it on the 4Runner, but I want to check with you before agreeing to have the throttle body serviced on the Venza. Is this service mandated by Toyota? – Gary

RAY: No. It’s not mandated by Congress, either, Gary, despite what you may have read in school about the Fartkowsky-Schnurrer Throttle Body Cleaning Act of 1915.

The throttle body is the device that regulates the amount of air that the engine is sucking in. When you step on the gas pedal, it sends a signal to the computer, which then sends a signal to a little electric motor in the throttle body.

That electric motor moves the throttle plate and allows more or less air into the engine – depending on the position of the gas pedal.

Over time, the inside of the throttle body can get crudded up with carbon, and that can make the throttle plate get sticky and close unevenly. But if your throttle body had enough carbon in it to make your throttle plate sticky, you’d notice it: You’d notice a rough idle, surging or hesitation and stumbling when stepping on the gas. But you didn’t mention any of those things.

Plenty of cars go their entire lives without needing to have the throttle body cleaned. So I’m a little skeptical that your dealer wants to do it to both of your cars. I think you might be getting YOUR throttle body cleaned, Gary.

If you’re interested, ask the dealer why you need your throttle body cleaned. If he tells you he just recommends it as preventive maintenance, tell him thanks, but you’d rather buy a year of HBO.

If he tells you he inspected it and saw carbon buildup, that’s at least a little more legitimate. But I’d still put it off until and unless you experience performance issues. It’ll cost you no more to clean the throttle body then, if that time ever comes, than it will cost you now.

Got a question about cars? Email Car Talk’s Ray Magliozzi by visiting the Car Talk website, www.cartalk.com.