It looks like the problem Toyota is having with "unwanted acceleration" is related to the drive-by-wire throttle control on models like the Prius.
If Toyota had used a cable, not only would the problem probably not have occurred, it would be simple to diagnose and easy to fix if it did.
A throttle cable physically connects the accelerator pedal to the engine's throttle. Pushing on the gas pedal increases tension on the cable, opening the throttle. Easing off the gas decreases tension, closing the throttle.
It's true a throttle cable can stick, causing the engine to race and the car to accelerate, if it happens to be in gear -- just as is apparently happening with the drive-by-wire system in some Toyotas. But the problem is infinitely easier to find and fix -- very much unlike the Toyota drive-by-wire system. Either the cable's sticking, or it's not. A quick physical inspection will determine this within minutes -- and the fix is as easy as greasing (or replacing) the cable.
In and out in 15 minutes.
Now, the thing with drive-by-wire is there may be nothing obviously wrong. You can't see a sticking drive-by-wire because there are no moving components to see. Just sensors and electronics. You're stuck chasing down the proverbial ghost in the machine -- who may not be cooperative. The problem may be intermittent or for all practical purposes, nonexistent. There are literally millions of "affected" Toyotas in circulation with the drive-by-wire system but only a small handful (a few dozen reported incidents -- at the time of this writing, at least) of actual "problem cars."
How do you deal with a problem buried deep in the software that manifests rarely and sporadically and for no apparent reason? Toyota engineers reportedly haven't been able to get the cars to do the Unwanted Acceleration Waltz under laboratory conditions that would enable them to nail down the source of the trouble.
It seems to "just happen" -- and the why is currently unknown.
But until the why is known, the problem can't be isolated, let alone fixed. Toyota engineers are left looking clueless while Toyota owners get to enjoy the relaxing sensation of driving around in a car with a possible mind of its own that may suddenly decide that more speed is needed -- perhaps at the worst possible moment, such as when a group of elementary school kids is walking across the road in front of you.
All because a simple, proven, effective means of controlling the engine -- the throttle cable -- was ditched in favor of a much more elaborate, computer-controlled means of doing exactly the same thing.
The question arises -- why? Why replace something that works perfectly well with something that (apparently) doesn't work nearly as well -- and which absolutely adds to the complexity (and thus, cost) of a new car?
No one seems to know. I've heard that it may have something to do with emissions control, because drive-by-wire is both more precise, as well as easier to tie into the computer brain that runs the whole car, than our old friend the throttle cable. It may also be easier to calibrate during assembly at the factory. With plug-in electronic components, it's easier to assure that every single car coming off the line is set up exactly the same way. With an old- school cable, there's more leeway and maybe a need for minor adjustments. One car's throttle "feel" may be slightly different than another's.
But we're talking "improvements" (with drive-by-wire) that are likely so minor that the average driver would never notice them. Back in the '90s or the '80s or even the '70s, complaints about throttle cables were rare and no one (that I recall) ever seemed to notice that (for instance) one '89 Mustang's throttle tip-in was just slightly different than the next one on the lot.
But we can't leave well enough alone, can we? We just have to have the latest gadget/technology, simply because it's possible. Nonexistent problems increasingly require elaborate -- and expensive -- "solutions" that no sane person would want, if given the choice.
This business may not kill Toyota but it's going to hurt it, badly. The automaker's main sales draw for years has been the safety and reliability of its vehicles and now that's out the window.
All because a perfectly functional component got tossed in favor of another bit of over-the-top technology that easily could have been done without.