uncommanded acceleration while using cruise control
While casually driving the 25 miles to my Father in laws with my wife driving I was getting frustrated with her foot... speed up, slow down, speed up, slow down... so I recommended energizing the cruise control. So she did. At the time I didn't put 2 and 2 together but now I know we were about to top a pretty good sized hill when the occurrence happened of course as things were continually going wrong in the seconds of the occurrence this wasn't at the top of my mind. As she set the cruise we must have been cresting the hill.... as we started down the other side we were expecting a mild speed increase and to see the cruise compensate by decelerating the vehicle for the downward run. Well to our horrific surprise the car began to accelerate and since we were going "down hill" the rate of this acceleration was quite significant! My wife begins to brake and I can tell we are decelerating but I can also tell the engine is not! At the bottom of the hill she is still braking with every fiber of her body pressed against the brake pedal and I can tell the brakes are about to fail..... I knocked the shifter into neutral and as the car now is actually stopping the engine begins to race into the red line immediately... ding ding ding it finally kicks me in the head we have a runaway accelerator which I quickly quill with the ignition switch. Now that we are safely on the side of the road and I am an experienced auto mechanic as well as jet aircraft mechanic I pop the hood and begin to explore.
What I find is the main accelerator cable has somehow become removed from the throttle body cable guide/pulley. The swedged end is still connected but the cable is now inboard over the shaft that connects the pulley to the butterfly shaft. I pulled slack into the cable reinstalled it into the cable groove over the pulley and calmly asked my wife to start the car. It started right up and idled like nothing had ever happened. I observed the cable as she revved the motor several time so I could see if there was a "cause" to it comming off the pulley to which I found none.
About a month later I was driving the car to work and was again topping a hill and setting the cruise and again the cable did the exact same thing!! Of course this time the engine was shut down much quicker and I was safely off the side of the road quicker. It was then when the ton of bricks fell on me and I amassed 2 plus 2 equals NEVER USE THE CRUISE CONTROL ON A HILL. Since then and since we no longer engage or disengage the cruise on hills we have had no more runaway accelerations! Although if the cruise is already on and working you can leave it on over hills without incident.
This leads me to believe the system generates some type of kick back allowing the cable to become removed from the pulley groove while the tension is at zero. A quick fix would be to add one or two cable guide pins around the pulley to prevent its misplacement during zero tension moments! Or like I said don't engage it on a hill. =)
uncommanded acceleration while using cruise control
While casually driving the 25 miles to my Father in laws with my wife driving I was getting frustrated with her foot... speed up, slow down, speed up, slow down... so I recommended energizing the cruise control. So she did. At the time I didn't put 2 and 2 together but now I know we were about to top a pretty good sized hill when the occurrence happened of course as things were continually going wrong in the seconds of the occurrence this wasn't at the top of my mind. As she set the cruise we must have been cresting the hill.... as we started down the other side we were expecting a mild speed increase and to see the cruise compensate by decelerating the vehicle for the downward run. Well to our horrific surprise the car began to accelerate and since we were going "down hill" the rate of this acceleration was quite significant! My wife begins to brake and I can tell we are decelerating but I can also tell the engine is not! At the bottom of the hill she is still braking with every fiber of her body pressed against the brake pedal and I can tell the brakes are about to fail..... I knocked the shifter into neutral and as the car now is actually stopping the engine begins to race into the red line immediately... ding ding ding it finally kicks me in the head we have a runaway accelerator which I quickly quill with the ignition switch. Now that we are safely on the side of the road and I am an experienced auto mechanic as well as jet aircraft mechanic I pop the hood and begin to explore.
What I find is the main accelerator cable has somehow become removed from the throttle body cable guide/pulley. The swedged end is still connected but the cable is now inboard over the shaft that connects the pulley to the butterfly shaft. I pulled slack into the cable reinstalled it into the cable groove over the pulley and calmly asked my wife to start the car. It started right up and idled like nothing had ever happened. I observed the cable as she revved the motor several time so I could see if there was a "cause" to it comming off the pulley to which I found none.
About a month later I was driving the car to work and was again topping a hill and setting the cruise and again the cable did the exact same thing!! Of course this time the engine was shut down much quicker and I was safely off the side of the road quicker. It was then when the ton of bricks fell on me and I amassed 2 plus 2 equals NEVER USE THE CRUISE CONTROL ON A HILL. Since then and since we no longer engage or disengage the cruise on hills we have had no more runaway accelerations! Although if the cruise is already on and working you can leave it on over hills without incident.
This leads me to believe the system generates some type of kick back allowing the cable to become removed from the pulley groove while the tension is at zero. A quick fix would be to add one or two cable guide pins around the pulley to prevent its misplacement during zero tension moments! Or like I said don't engage it on a hill. =)
- Jeff A., Columbus, MS, US