A few months ago, I read a story about Toyota owners who claim they experienced "unintended acceleration," otherwise known as a "runaway" condition. In simple terms, the car took off without the driver stepping on the gas or, it kept going after the driver took his/her foot off the accelerator pedal. Obviously, a very scary and dangerous situation. Apparently, there were enough drivers reporting this scenario to force Toyota to issue a recall that affected 4.2 million vehicles. It required dealers to remove the floor mats from the affected vehicles and alter the gas pedals, the theory being that the gas pedal was getting caught on the floor mat and causing the engine to race. This "fix" was found to be suspect; as ABC News reported on Jan. 21, 2010, "on the day after Christmas, four people died in Southlake, Texas, a suburb of Dallas, when a 2008 Toyota sped off the road, through a fence and landed upside down in a pond. The car's floor mats were found in the trunk of the car, where owners had been advised to put them as part of the recall."
As some of my regular readers know, I was an auto mechanic (they're now called technicians) for twenty-eight years. During the late 1970s, the National Institute of Automotive Service Excellence (NIASE, later shortened to just ASE) began offering tests to certify technicians in eight different categories; I voluntarily took and passed 16 hours of tests to become certified in all categories. When my back began to give me trouble, I became a service manager and service advisor with several car dealers for another sixteen years until my retirement in 2006. The only reason I mention all of that here is to give you some idea of my background and experience.
The problem Toyota (and their customers) are currently having could be caused by any one of a number of things. There are mechanical components (pedal, hinges or pivots, cables, links, etc.) and electrical components (sensors, switches, wiring, etc.) that could be at fault. Eventually, the problem will either be fixed by finding the faulty part and replacing it with something new or by changing parts until the condition no longer occurs.
All of this seems eerily familiar to me and to anyone who owned an Audi 5000 back in the 1980s; sometime during those years, a similar condition was reportedly happening to those cars. I worked for a Porsche/Audi dealer from 1979 to 1990 and was a certified Porsche and Audi technician during that time when the problem first came to light. And, though I don't know too much about Toyotas, I DO know quite a bit about those Audis.
I had never read anything in the newspapers about the "runaway" Audis that drivers claimed to have experienced until we received the first recall addressing the problem. We were told to remove the "Coco floor mats" (as they were called) and replace them with something new. The original floor mats, it seemed, were a kind of heavy woven substance resembling twine. When they got worn, from drivers' heels digging into them and pivoting between the accelerator and brake pedal, the strands became torn and very loose. The thought was that the gas pedal (which had a cylindrical metal knob on the underside) was getting caught in the worn floor mats.
Around the time of the first recall, we were also instructed to check the accelerator cable and linkage for binding and insure that necessary points were lubricated properly to prevent sticking. It was also about that time when I first began hearing reports of people having serious "runaway" Audi problems. One owner supposedly ran through the back wall of her garage and seriously injured her own child on the other side. On another day, an Audi was brought in on a tow truck; the back of the car was smashed in so that the rear bumper was nearly even with the rear window. We were told the driver lost control and the car and fell backwards down several stories of an open elevator shaft in a parking garage.
Shortly afterward, another recall was announced; this one had us putting a plastic shield on that cylindrical metal "knob" on the bottom of the gas pedal. Then, another one had us drilling two holes in the brake pedal and installing a one-inch "spacer" to make the surface higher. It was thought that the gas pedal and brake pedal were at roughly the same height and that people were confusing the two pedals, hitting the gas when they should have been stepping on the brake. Throughout all of this, no one I knew (and none of my fellow technicians) had ever experienced a "runaway" condition on any of the cars we worked on... and, we worked on a LOT of Audi 5000s. In those days, those cars had a LOT of problems.
Then, one day, I was handed the repair order for a customer's car to be worked on; there was no complaint of a "runaway" condition. It was brought in for other work (tune up, oil change, etc.) I found the car in our parking lot, got in and turned the key to start the car. I stepped on the brake and shifted the car from "park" to "drive." And, then it happened... the engine raced and the car lunged ahead. My immediate reaction was to press on the brake with both feet; that stopped the car with the engine under a full load. I didn't want to shift into "neutral" just yet because I didn't want to disturb anything without trying to find out why this happened. I bent over and extended my right arm down, grabbing the gas pedal with my right hand; it wasn't caught on anything. The pedal just flipped up and down as if it wasn't attached to anything. At that point, I turned the key and shut the engine off. I put the car back into "park" and restarted it; the engine was now running perfectly. I put the car into "drive" and drove the car as if nothing had ever happened.
After bringing my "runaway" Audi into the shop, I reported what happened to my service manager. He, in turn, notified the main offices of Audi who sent a team of experts to the shop the next day. They went over every inch of that car but never found anything wrong with it and the car's owner never reported another problem with the accelerator.
So, what do I think happened? The way the accelerator was designed on the Audi 5000 was that a cable ran from the accelerator pedal down under the car to a lever on the outside of the transmission. From that lever, a metal rod ran up to the fuel injection throttle body on the top of the engine; the throttle body regulated how much air was mixed with fuel (from the fuel injectors) and, ultimately, how fast the engine would turn (and how fast the car would go). The lever on the outside of the transmission was connected to another link on the inside; that was connected to the throttle valve in the valve body of the transmission. As you depressed the gas pedal, the throttle valve moved and caused the throttle pressure to increase inside the transmission. On the output shaft of the transmission was a governor; it was measuring the actual speed of the car and controlling the governor pressure inside the transmission. In simply terms, depending on the throttle pressure and the governor pressure, the car would shift from one gear to the next at different points. Got that so far?
Now, the most obvious cause of a "runaway" Audi would have been if a large stick (or other debris) on the road got caught under the car and caused that solid rod (from the transmission lever to the throttle body) to be moved upward. That would have caused the throttle body to be moved to an accelerated position independent of the gas pedal. That did not happen to me on that car in the parking lot; there was no debris of any kind under the car and yet the pedal felt like it was not attached to anything. (On Audis with Cruise Control, the accelerator linkage also passed through another part. Theoretically, a malfunction in that unit could have caused the accelerator link to the throttle body to stick as well. There was the possibility that a mechanical or electrical malfunction in the cruise control system could have caused the problem; but what about cars without cruise control?)
My specialty as an Audi technician was rebuilding the transaxle assembly; this included the differential (final drive) and the previously mentioned transmission. These units were connected together and had one major flaw: fluid from the differential would leak into the transmission and contaminate the transmission fluid with gear oil. Most owners never knew anything was wrong until one day the transmission would just quit. There were a couple of other techs in the shop who repaired these transaxle assemblies but I believe I did 90 % of them. I probably averaged three transaxle overhauls per month for about eight of the eleven years I worked there (maybe 350 of them)! And, what I discovered during that time may well be the cause of the "runaway" Audis.
Inside the transmission, the link that controlled the throttle valve was interlocked with it by way of a groove on the throttle valve that the link fit into. If you moved the gas pedal, the cable moved the (outside) lever and the (inside) link moved the throttle valve. But, the throttle valve had several "ports" through which it directs fluid within the valve body. Imagine if excessive pressure within a port of the valve body inadvertently acted upon the throttle valve and caused it to move forward; because it was "locked" to that link, it could have caused the rod to the throttle body to force the engine to race, creating the "runaway" condition.
Far fetched theory? Well, what would you say if I told you that Audi changed the design of that link and throttle valve during the time that everyone was complaining of "runaway" Audis? Because that's exactly what happened. Without any fanfare or announcement related to the "runaway" problem, we were suddenly instructed to replace the valve body every time we overhauled a transaxle assembly. And, since so many Audi 5000s had the transaxles repaired (for that leak between the differential and transmission) a LOT of Audis got new valve bodies.
So, what was the difference? Instead of that link being firmly "locked" into the throttle valve, the new throttle valve (that came with the new valve body) had that link pushing against the throttle valve. When the accelerator pedal was released, and that link moved back away from the throttle valve, a newly-added spring kept the throttle valve mated to the position of that lever/link. In this way, if anything inside the transmission caused the throttle valve to move, it would not have dragged that link along with it and, consequently, the linkage to the throttle body affecting the speed of the engine.
The cause of the Audi "runaways" was never formally disclosed. I think the problem just slowly began to go away and less and less attention was paid to it until no one talked about it anymore. I suppose from time to time the driver of any car could experience unintended acceleration; but if no problem is found during a subsequent check, the cause will probably be attributed to "driver error."
Of course, I don't know if any of this has anything to do with the problems experienced by the Toyota drivers. But, knowing what I DO know, there is probably a part that is malfunctioning and will cause more injury and death until the mystery is solved. I have located some generic diagrams depicting how the valve body and related parts work in an automatic transmission which I will include below. (Click on any image to enlarge.) To read the story in simple terms, go to http://eng.kaps.cz/news/understanding_the_valve_body_1_2-982.html)
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