Is mechanic’s throttle body recommendation legit?

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. 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 no thanks. If he tells you he inspected it and saw carbon buildup, that’s 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.

Instructions for doing your own shock absorber ‘bounce test’

Dear Car Talk:

My 2004 Jeep Grand Cherokee has 187,000 miles on it. I bought it new. What is a reasonable lifetime for shocks? I've been told to keep them if they aren't leaking. Mine don't have signs of leakage, but the car does not ride as it first did. I've replaced the tires with ones with softer sidewalls, and have replaced the springs. Both have helped the ride, but should I be replacing the shocks as well? Many thanks! – Jon

RAY: Jon, you should have written to me five years ago.

Actually, there’s no time limit on the life of a shock absorber; its lifespan depends on how much and what type of use it gets. If you do mostly highway driving, it’s conceivable that your shocks are still OK. It would be unusual, but conceivable.

Since the shocks aren’t leaking, then you have to give them the classic “bounce test”: You start at one corner of the car, and push down as hard as you can on the bumper. When you’ve pushed it down as far as you can, let the bumper come back up and immediately push it hard again – trying to amplify the movement. It’s like pushing a kid on a swing. The idea is to really get that corner of the car oscillating up and down as violently as you can.

Then, when it’s really moving – or when you begin to feel the first signs of angina, whichever comes first – push it all the way down and let it go. If the shock is good, that corner of the car will come back up once and stop immediately, and not oscillate. If it continues to go up and down at all, the shock is worn out.

I have to say that we replace shocks far less frequently than we used to. We used to routinely replace shocks at 30,000 or 40,000 miles. And now it’s not at all unusual to have cars with well over 100,000 miles that still don’t need replacement shocks.

Still, I think you’re at the far end of the bell curve, Jon. And even if you replace the shocks, you can’t reasonably expect the car to ever ride as it first did. Remember, it’s 13 years old – old enough to have pimples and a first girlfriend. So pretty much everything is somewhat worn out.

So if you want a new-car ride, look at the 2018 Grand Cherokee. But in the meantime, give your shocks the bounce test. Good luck.