Electronic Design
Bob’s Mailbox: More Mail About Unintended Acceleration

Bob’s Mailbox: More Mail About Unintended Acceleration


I remember riding with my dad in our 1963 Chevrolet wagon. I believe it was a Bel Air. The accelerator suddenly went to the floor, with no desire to come back up. Dad did just what you suggest, and turned the car off. Of course, in those days, power steering and power brakes were really options, and I don’t remember if our car had them. It probably didn’t have the locking steering column. We pulled over and opened the hood. The throttle mechanism had a good sized spring that applied the return pressure. That spring had come loose. \\[Check. Of course. /rap\\]

We fortunately found it sitting in the engine compartment and were able to replace it. Dad finished our errand driving rather gingerly, and then we got a new spring and made the mounting more secure. \\[Tie the spring to its connections with fine copper wire. /rap\\] I wonder how common that condition was back then.
- Earl Erickson

Probably pretty common. Thanks for the comments. Beast rgrds. /rap

Hello Bob,

Some years ago, around 1992-1993 I think, I was driving a rental vehicle to work because my own was in the shop. I believe it was one of the early Izuzu Troopers that still looked like they had been partially run through a car crusher applied from the side. Technically, I suppose you would call it a poor wheel base to height ratio.

Anyway, I had driven this thing on the freeway for maybe 15 minutes and tied up nearly to a standstill in traffic when I felt the accelerator pedal moving away from my foot. I instinctively stepped on the brakes and started generating a smokescreen you wouldn’t believe and attracting lots of gawkers. Shortly thereafter (very shortly), I put it in neutral, shut off the key, and glided to the side of the freeway. \\[Good man! /rap\\]

I sat there for about 20 minutes recovering from the shock and trying to figure what to do. I had even at that time heard a few stories of unintended acceleration, and being slightly familiar with thermal runaway effects in electronic devices, I acted on a hunch \\[Good hunch. /rap\\] and tried an experiment to see if this might be what was going on.

So, I let the engine cool off for a while and then restarted it and started slowly driving down the freeway. It was initially okay, but after a few more minutes, it started to show the same behavior. This time I was ready and pulled over to the side and shut off the engine.

After another 10 minutes, I started up again and got several more miles under my belt before it acted up again. It was becoming predictable so I repeated this process probably half a dozen times more before I finally pulled into the parking lot at work. \\[And what made you suspect something was wrong? /rap\\]

I immediately called the rental company to bring me another vehicle and explained what I was experiencing. The young man thought I was either crazy or drunk, but eventually agreed to bring the other vehicle. \\[Good man. /rap\\]

I naturally cautioned him about the nature of the problem, how to watch for it and what to do when it started manifesting. I think he still thought I was crazy but went on his merry way. I never heard back from them about it. So, that’s how I became a believer in unintended acceleration! \\[Wise fellow. /rap\\] It never happened to me again, though.
- Paul Jones

Yeah, because you never drove that ratty Isuzu again. Thanks for writing. Beast rgrds. /rap


Back in the early days before cruise control (early 1960s), I purchased kits and installed them on my cars and always was careful when connecting up the vacuum operated actuator to the throttle linkage. I never had a problem but was so glad that the option become available so I could spend more time on other similar and somewhat questionable projects I think of as hobbies.
- Bob E. Morley

I designed an inside-my-head Cruise Control (see “What’s All This Cruise Control Stuff, Anyhow?” at www.electronicdesign.com). It worked as I planned it—and I still didn’t like it. It boxed me at a constant speed, into traps in traffic, where I’d have to slow down and maneuver around slow traffic. I’m better off controlling my own speed and avoiding traps.

Out on I-280, cops don’t care if you are going 60, 65, 70, 75, or 85. (I’m not sure about 90.) I don’t go over 80 unless there is a serious problem or disaster. So, I don’t need a cruise control to keep me from getting a ticket. (That may not be true everywhere...) So if I had a real store-bought cruise control, it wouldn’t do what I want.

Beast rgrds. /rap

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