RUN-AWAY CARS, I think I might have the answer - not stuck pedals, not floor mats - catalytic converters do it! Several years ago I was driving my Subaru when the engine started to race. I put it in neutral, pulled over, and opened the hood. The catalytic converter, just visible, was glowing cherry red. After a few minutes it cooled off and the engine stopped. I was puzzled but decided the manufacturer had installed a sensor that would keep the engine running while the accumulated stuff in the converter burned off. I got back in the car and drove home and didn’t give it another thought until a few days ago - then like a light going on in my head, I made the connection - it fits what I have been reading and hearing about Toyota drivers, especially those who said there was no floor mat and the pedal had not stuck when their engine started to race. Now you will say “how could fumes entering the engine on the exhaust stroke possibly cause the engine to run fast and out of control?” That doesn’t make sense, I know, but it happened to me. I saw the engine racing while the catalytic converter was cherry red and quit when the converter cooled. If I am on to something, Toyota and the public need to know.
Here is the only explanation I can come up with. My research deals with pressure and so I know a little about the subject. The very hot (cherry red) catalytic converter could cause considerable pressure for a matter of minutes, especially if the exhaust system is small or partially plugged and the contents of the converter are rapidly vaporized by the intense heat. It seems to me that if through some design flaw or worn parts both exhaust and intake valves are open simultaneously at the end of the exhaust stroke, even for a split second, pressurized fumes of unburned ?fuel? from the hot catalytic converter (we know they reside there) could find their way through the pistons and into the fuel/air manifold and then be drawn back into the engine and ignited either by spark or compression. Of course, the pressure would have to be great enough to drive the real exhaust out through the air intake to get rid of it. (I think I had turned off my ignition when this happened to me, but I can?t remember.) If this explanation is right, then the engine would run quite normally on those fumes in a forward direction. I have had experience with the engine running backwards in my old Model A Ford as I intentionally filled the muffler with unburned fumes, so I know that that is a possibility as well (not smart as I learned from having to replace a muffler popped wide open, but I was a kid and did dumb things like that). All of this is sufficiently bizarre that it occurs to me the Toyota engineers and others investigating these weird accidents may simply not have tumbled to the possibility of this being the explanation. I would say it just couldn?t happen, but why else would my engine race uncontrollably while my catalytic converter was red hot? That is what I witnessed. I welcome your responses.
Your cat was red hot because of a lot of unburned (rich) fuel going through it being converted to CO2 and H2O. It’s a symptom of whatever problem you had, not the cause. I saw the same thing on a Dodge Omni I was following years ago, a red glow under the car from the cat.
Sorry, but that theory doesn’t work at all.
Like the others, I believe that the OP is confusing cause and effect.
The cat converter was not the cause of the racing engine, but was the effect of whatever problem caused the engine to race.