What could be causing acceleration before stopping?

  • Ray Magliozzi
12:00 a.m. Friday, Oct. 27, 2017 Cars

Dear Car Talk:

I just bought a used, 2010 Lexus GX 460 with 110,000 miles. It has an unusual problem: As I brake to approach stop signs and stoplights, the engine accelerates slightly. The engine speed will increase from 750 rpm to 1100 rpm for a brief second or two as I come to a stop. After spending almost $200 to clean the throttle body (to no avail), I thought I should check with you and see what else to dig into. – Terry

RAY: The next thing to dig into is your wallet, Terry. Because you’re a Lexus owner now.

Actually, I have three ideas for you. I’ll give them to you in order of likelihood – least likely to most likely: Idea No. 1 is that your feet are swollen, and you’re accidentally scraping the gas pedal when you hit the brake. Look, I said I was going to start with the least likely idea.

Idea No. 2 is that you have a failing power-brake booster. If there’s a vacuum leak in the booster, when you step on the brake, the drop in engine vacuum could fool the car’s computer into thinking that you’re stepping – very slightly – on the gas pedal. In other words, if the engine experiences a reduction in vacuum, that’s like adding more air. And when the airflow sensor reports that more air is coming in, the computer responds by sending in more gasoline.

Idea No. 3, which I think is the most likely, is that all you’re experiencing is a downshift. As you slow down, the automatic transmission downshifts into its lower gears. And just before you come to a stop, it shifts from second gear into first. That sends the engine speed up a few hundred rpm, which is exactly what you’re reporting.

I don’t remember that last downshift being noticeable on any of the Lexuses I’ve driven lately, so it could be that you need to go to the dealer and see if you can get a software update for the transmission.

You can do a little bit of diagnosis on this yourself, Terry. If it’s the power-brake booster (Idea No. 2), you should be able to reproduce the problem while idling in park. So try that.

If you can make the problem occur only when the car is actually moving and slowing down, then it’s more likely to be the transmission downshifting (Idea No. 3).

And if it’s neither of those, cut down on the salt, try a diuretic and see if you can fit back into your size 11s (Idea No. 1). Good luck, Terry.

Satisfying old-car fetish depends on safety

Dear Car Talk:

My wonderful husband, Bill, 76 years young, is having some kind of an old-car fetish crisis. While I am not jumping for joy about this, I am not totally opposed, either. My questions are more about safety and reliability. Here are the cars he’s looking at: a nice-looking, restored 1951 Willys Jeep Station Wagon with a Mustang engine, transmission and rear end; a 1972 Ford F-100 pickup with a V-8; a 1979 VW Bug convertible; and a 1988 Toyota Land Cruiser. My question is: Which of these would be the safest/least dangerous? Thanks very much. He is a great fan of “Car Talk,” and will respect your answer. – Roi

RAY: They always promise they’ll respect us after the answer, Roi.

I’m going to lean toward the Land Cruiser. Your primary question is about safety, and I think the Land Cruiser, due to its size, weight and higher seating position, would be the least dangerous of the options you list.

Forget the ’51 Willys. While it’s true that steering and brakes had been invented by the time they designed that vehicle, Willys didn’t make a wholehearted commitment to the technology.

And forget the VW Bug. That car would be the underdog in a collision with a size-13 cowboy boot.

The ’72 Ford pickup is fairly substantial, and I do like it for its simplicity. It’d be relatively easy to fix, and the cost of repairs wouldn’t wipe out your retirement savings every time you need brakes.

But the Land Cruiser is a beast. And since your question was which one do I think would be the safest, I think the Land Cruiser has the edge. Even better, if he’d be willing to go as far as the Clinton administration era, he could get himself a Land Cruiser with an air bag (’95 was the first year). Then he could crash all he wants.

And while the Land Cruiser is expensive to repair, that might hasten the process of Bill getting sick of this whole old-car thing, and get him to go back to his 2009 Camry, which is safer than any of these heaps.

Good luck to you and Bill, Roi.

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