Sudden Acceleration

Strange sudden acceleration problem. Ideas?
I was backing up by large equipment trailer with my original owner 2002 Tundra Limited. Truck has 119,000miles. I was backing up the slight grade driveway into the graveled trailer parking spot alongside the driveway. As the truck was entering into the gravel area and starting to spin gravel I put the truck into Low 4WD and once again resumed backing. After a few more feet the truck stopped movement as if I hit a curb but nothing was in the way. The front wheels were now just slightly on the hardtop and mostly on the gravel. Increasing the accelerator pedal did not move the truck and the engine speed barely increased if at all. Let off and tried again but got same results. Looking back, possibly I may have been in a 4WD differential bind but have no certainty. Pushed the accelerator pedal again and suddenly I heard a loud "Pop" and the trucked raced at a high rate of speed backwards. I knew the moment of the Pop and movement I took my foot off the accelerator but I did not stab at the brake as I was facing rearward and fearful I might stab the accelerator instead by mistake. I expected the truck would slow as it was going uphill but it raced. It was only one or two seconds and only traveled probably twenty feet but the speed was astounding and the damage down was incredible. The trailer jacknifed and swung around. The trailer coupler was bent and ripped off. The safety chains tore off. The 24 inch steel bar side of the trailer folded band broken. The truck ultimately overturned onto its side in the gravel and the truck motor stopped immediately then. The truck is most likely totaled. The bed is torn open like a can opener hit it and bent all to sh*t. The driver side rear spring perch is twisted. The bumper looks like a pretzel. An 18 inch slash cut through the rear Michelin and destroyed one of the newly installed TRD wheels. The passenger side where it came to rest on busted the glass and damaged the front fender, main door, mirror, access door and right side of the the bed. This thing took of like a rocket and I can not imagine this much damage in such a short distance. I realize low range is power (torque) but the speed was much more like 2 WD high than 4 WD LOW. I have driven this truck since new. What in hell happened? How can the speed get up that quick in 4 Low? What was the "Pop" sound when all hell was unleashed? Could I have had it in 4x bind that just happened to release? Could it somehow have popped out of 4 x low into 2 High? The wrecker driver who uprighted it also verified the 4x "Low" Button still pushed in. I just this morning changed the flat tire with the spare and took it up the neighborhood street and it drives in the 2 WD range with the steering wheel cocked at 15 degrees and a lwhole lot ot of moaning underneath. What did I do or what could have happened? Definitely not new to the truck or 4x4 (Owned Toyota 4x4 since 1988) but this was the first time 4x4 was exercised in a year. No injuries (other than pride) and truck was insured.

 

Dammit man, that sucks. So the engine continued to rev after you let off the throttle? Throttle cable still intact? If you move the throttle plate by hand is it in a bind or sticky?

 

Ooof. Total bummer! If I had to venture a guess, I think you answered your own question. It sounds like it was indeed binding in 4WD low - assuming you had the wheels turned. Once the drivetrain unbound itself, it was like you were power braking and launched hard (there is energy stored in the torque converter when the engine is revving but the transmission output is stalled). One of the fun things about 4wd low is that because of the gear reduction, the brakes have to work harder to to bring the vehicle to a complete stop.

The only other thing I can think of is a bound/sticking brake on the equipment trailer. Depending on how heavily loaded it was and how much angle you had in the trailer, the axles (assuming it was tandem axle) can get a little bent out of shape and possible bind the brake shoes. Or they can just stick. Kinda spitballin here. Either way, that is just the worst...

 

That blows, 2002 with only 120K. Thing looks like it was in nice shape also. The bind up sounds legit, it happened to me years ago on a silverado but i wasnt near anything so no real issue besides scaring the crap out of me.

 

Damn dude.... sorry for your loss.
Looks like it was a nice rig, love that color too....

 

I hope no one saw it happen.

 

Not sure why it wasn't engaging in gear, but as far as acceleration, Toyota was having issues there for a while because people weren't using the supplied plastic hook for the driver's floor mat, and it was getting wedged up in the pedal, causing exactly what you mentioned. To the point there's warnings everywhere, "Always use the hook", and every TSB Toyota published after the fact which required touching the floor mats also warns it's mandatory to use the floor hook with the mat. And all modern form-fit floor mats include this warning (all I've ever used). Was stuck accelerator a case of "didn't have the floor mat hooked"?

Sorry about the loss. What a damn bummer.

 

I think that hook issue was newer models than the 2002.
like 07-09 years

 

It definitely became an "identified problem" then (I think they called it pedal trapping or pedal entrapment, officially?), but a shifting floormat in any vehicle can mess with pedals using DBW.

 

Just Googled it, Cars.com has a great writeup. https://www.cars.com/articles/explaining-the-toyota-floormat-recall-1420663233094/

Looks like it was as early as 2005, and Tundra was included starting in 2007, but when I looked, the pedal design of the '07 second gen appears similar enough to the 1st gen DBW system that it should/would be impacted as well.

https://media.toyota.ca/en/releases...pedal-on-select-toyota-division-vehicles.html

That's about as far as I've got time to look.

Actually a quick edit to add more. I see the 1st gen is clearly not excluded from the NHTSA recall, so quite possibly affected. The document gives a wide array of things to look for that would caue a vehicle to be added, but the exclusion list has no Tundras.

​

 

Did the trailer have surge brakes?