This could be very dangerous: throttle cable

w261w261 · #1 07-26-2008, 04:00 PM

I posted this as part of another thread, but thought that I would start a new one, as this could have been pretty bad.

My son's '92 tried to run away from him, and the reason was the throttle cable had been compromised. What had happened was this: the cable comes out of the firewall, makes a turn to starboard, and then turns again to head straight in to the throttle. It is clipped to the cruise control throttle cable with a figure-8 plastic thingy. Over time, the throttle cable had moved such that it did not head straight into the "winder," but came in at an angle. It gradually developed a sort of kink in some of the individual wires. This kink, which manifested as a bump of sorts in the cable (reminded me of a ply separation), eventually got big enough so that it caught the flange of the "winder" when the throttle was released. Bingo, and a real puckering experience.

When I looked at it, I also noticed that the cable was about to fail right behind the adjusting nuts, but the failure was hidden by the cover. When I installed the new cable, I made sure that the final turn was a nice sweeper, and the figure-8 clip held the throttle cable below the cruise cable. It seemed happy that way.

Install of the new cable was tedious but straightforward, as I'm 6'3 with big hands and need reading glasses. You order the new cable ($48), disconnect it from the throttle body, take out 4 bolts that hold the accelerator pedal to the firewall, push in the ears on the square black plug that holds the cable to the pedal, and pull the whole thing through into the cabin. Now take the new cable and attach it to the pedal (it's loose at this point) by pushing in the square plug. Feed the engine end of the cable through the hole in the firewall, go around to the front and pull it some so the firewall plug seats, go back inside and rebolt the pedal. Attach at the throttle body, adjust and you're good to go. The worst thing is the cramped quarters.

Needless to say, something like this could end up as a real bad experience. I'd suggest that you all take a minute and look at the throttle cable, and make sure that it sweeps in straight to the winder.

w261w261 · #2 02-02-2010, 07:27 AM

I'm going to bump this up because of all the press about Toyota.

The reason my son's throttle cable failed, leading to a stuck throttle, was that whoever had installed it had not put a nice radius on the final sweep into the throttle body "winder." I would suggest everyone check to make sure their cable goes in straight and doesn't have that kink, which led to fraying and a dangerous situation.

Mike621 · #3 02-02-2010, 08:00 AM

I had the very same problem developing on my Claret (now approaching 186,000 miles). However, I too am replacing it with a new one from Subaru, among other things.

Trevor · #4 02-02-2010, 06:30 PM

This is a very wortwhile thread.

As a result of the issues involved, and the fact that I have been deeply involved with control systems, the new “fly by wire” set ups worry me. Have they got it right? Is anyone here aware of the details?

Hondasucks · #5 02-02-2010, 10:06 PM

The deal with the Toyota sticky throttles (of which there have been less than a dozen cases!) is condensation inside the potentiometer in the pedal sensor causing it's resistance (to movement, not electrical resistance)to increase to the point where the return spring can no longer overcome it, so the pedal doesn't return to the idle position when released.

Trevor · #6 02-02-2010, 10:29 PM

Quote:

Originally Posted by Hondasucks

The deal with the Toyota sticky throttles (of which there have been less than a dozen cases!) is condensation inside the potentiometer in the pedal sensor causing it's resistance (to movement, not electrical resistance)to increase to the point where the return spring can no longer overcome it, so the pedal doesn't return to the idle position when released.

Special thanks for the exact and well detailed information. Very interesting.

I am not surprised. The problem is typical of automotive electrical systems.

When designing industrial control systems, I have always made very sure that where safety is involved, the mechanical operation of any sensing device is absolute. Where a potentiometer was involved, it would have been interlocked with an independent secondary limit switch, for very good reason.

Thanks, Trevor.

Elliott · #7 02-02-2010, 11:04 PM

Quote:

Originally Posted by Hondasucks

The deal with the Toyota sticky throttles (of which there have been less than a dozen cases!) is condensation inside the potentiometer in the pedal sensor causing it's resistance (to movement, not electrical resistance)to increase to the point where the return spring can no longer overcome it, so the pedal doesn't return to the idle position when released.

I'll stick to my barbaric mechanical throttles. The main reason they do this now is for traction control, instead of retarding the timing and killing the power, it closes the throttle a little if it decides you pressed it too hard. Not like these things really help much, all of the "driver aides" in the world don't help a terrible driver.

Saw it today, we get a little snow and ice down here, no one knows how to drive. I watched someone in a very new Honda CRV with AWD and everything fail miserably trying to get past a couple 20-30 foot patches of ice on the way up a small hill. I could see the AWD and traction control fighting for traction that just wasn't there, dunno where she got the idea that AWD means you magically get traction if all 4 tires are on ice. Only reason there was ice still there is because of the culverts running under the road and the shade from the trees, there was plenty of clear road before and after the ice, just need a little momentum, which she didn't have because she was trying to creep up there at 5mph. I didn't have a single issue getting up there in my 1975 Gremlin, just a little wiggle of the rear end as I went over the ice, only "driver aide" on that car is power steering, I even have manual drum brakes.

Hondasucks · #8 02-04-2010, 12:21 AM

Quote:

Originally Posted by Elliott

I'll stick to my barbaric mechanical throttles. The main reason they do this now is for traction control, instead of retarding the timing and killing the power, it closes the throttle a little if it decides you pressed it too hard.

The other reason is for emissions and fuel efficiency, when you slam the throttle wide open (or just abruptly open or close the throttle) it takes a little for the engine to "catch up", with the "throttle by wire" the computer can more effectively manage the engine.

As for the limit switches, etc.. that doesn't do much good in this case, since the problem isn't really the throttle sticking wide open, it's it not returning to idle when released. The other problem they are having is with the gas pedal on certain models hanging up on the floor mat, but most of the cars that hang up is cuz people will buy the all-weather rubber floor mats and stack them on top of the stock mats, making the stack tall enough for the mat to catch the pedal. (The solution here that I've heard about is in ECU update that will cause the computer to close the throttle if it detects throttle and brake input at the same time.)

Elliott · #9 02-04-2010, 01:57 AM

Quote:

Originally Posted by Hondasucks

The other reason is for emissions and fuel efficiency, when you slam the throttle wide open (or just abruptly open or close the throttle) it takes a little for the engine to "catch up", with the "throttle by wire" the computer can more effectively manage the engine.

So pretty much the same effect that vacuum secondaries (or mechanical secondaries with vacuum air doors in the case of a Q-jet) and dashpots had on cars with carburetors.

I'm sure they work fine 99% of the time, but I don't like the idea of my right foot doing nothing more than giving a suggestion to a computer.

kwren · #10 02-04-2010, 02:14 AM

Quote:

Originally Posted by Hondasucks

The deal with the Toyota sticky throttles (of which there have been less than a dozen cases!) is condensation inside the potentiometer in the pedal sensor causing it's resistance (to movement, not electrical resistance)to increase to the point where the return spring can no longer overcome it, so the pedal doesn't return to the idle position when released.

Toyota claims that all this sticking is on 2010 models.
That would be pretty fast condensation inside the potentiometer in the pedal sensor causing it's resistance to increase to the point where the return spring can no longer overcome it.

Even Toyota doesn't believe this "fix" will fix it, just buying time. It is a software problem...

Keith

Cam · #11 02-04-2010, 12:48 PM

Quote:

Originally Posted by kwren

Even Toyota doesn't believe this "fix" will fix it, just buying time. It is a software problem...

Keith

Where did you get this information? The problem is with the movement of a potentiometer, meaning it is mechanical. They are just writing program for a fail-safe into the ECU to try and make it less dangerous.

Trevor · #12 02-04-2010, 01:26 PM

Quote:

Originally Posted by Cam

Where did you get this information? The problem is with the movement of a potentiometer, meaning it is mechanical. They are just writing program for a fail-safe into the ECU to try and make it less dangerous.

Thank you Cam,

I was about to make the same point, but did not do so as I am continually copping flack for correcting wrong posts, even though wrong information is not in the interests of members.

What annoys me, is that those involved, do not pass an opinion and advise on the basis that they have authority.

kwren · #13 02-06-2010, 01:44 AM

Quote:

Originally Posted by Cam

Where did you get this information? The problem is with the movement of a potentiometer, meaning it is mechanical. They are just writing program for a fail-safe into the ECU to try and make it less dangerous.

Sure...

Keith