I'm not saying the Jag would take off. But I could see the engine overpowering the comparatively weak rear brakes and causing a burnout (rear wheels spinning with no front wheel movement).

Hell, even when I drive up on ramps (with the front wheels on the ramps), the ramps slide on the concrete floor and I have to push the brakes much harder than I'd expect to get the rear brakes to stop the car!

 

I'm with you 100% there, Alan. I was just trying to dispel the idea that normally functioning brakes would not hold a car stopped, even if the throttle was at full. Experience shows they will.

Cheers,

 

Strange! I would check for a broken engine mount. If the engine is not held solidly by the mounts, the engine can lift caused by torque. In doing so, without a solid connection, the throttle can be forced further open. The further it is opened the more force causes it to open more, and faster. Shutting the engine off is the only way to stop it.


Just a thought.


Peter

 

On the cars in this forum? Is that a theory (guess) or fact? I ask because a wider open throttle (if possible) than commanded by the PCM will first result in the PCM reducing the current to the throttle motor and if that fails to close it then a code and rapidly limp home / restricted performance.

I'm working on the basis that these are drive-by-wire cars (throttles) like the S-Types.

(I'd be surprised at such young cars having broken mounts.)

 

I had it happen with a broken motor mount in an Impala SS 396 Chev that was less than 6 months old. Just a thought!

 

Yes, there was a recall on that one from GM involving installing a restraint strap to the left upper control arm. Or at least there was for the 427's.

But the Impala had a mechanical throttle linkage.

Jaguars of later years are all drive by wire and do not use any rod linkages, only a bowden cable to drive the throttle position sensor and act as a failsafe.

 

the same exact thing happened to me on my 2008 xkr.
i was waiting on a stoplight when all of a sudden the car started
accelerating. I HAD to increase the pressure on the brakes to keep the car from moving and all the while the wheels were squeelling had to put it on neutral then the rpm really shot up. thought the engine would blow but it went back to normal idle rpm. no floor carpet issues or accidental stepping on the gas.
saw something on the internet about tin whiskers and signal interferance.
I did bring it to a mechanic a few weeks ago before the incident about how the idle would be erratic while being warmed up going above 1200 rpm while on park. he scanned it but didnt find any codes.
to all of you who have experienced this, its not a figment of your imagination.
just because jaguar said they cant find anything wrong doesnt mean it aint broke or even scarier they do know somethings wrong and wont tell you because the liabilities may be too high.

 

had the same exact experience as Bogeymanii
in a 2008 XKR at a stoplight so it's true. It is happenning
no issues with floor carpets or stepping on the gas pedal by accident.
Found something in the internet about signal interference
and Tin whiskers shorting out circuits. Jaguar won't admit anything is wrong
so what can you do. found some people in the internet suing jaguar about this issue

 

Do the pre 2010 cars have dual throttle position sensors in the gas pedal position sender unit? I know the 2010+ cars have dual sensors and if they don't agree it will throw a code and probably go into limp mode.

 

I know every single time I've had unintended acceleration something was caught on the throttle pedal, most often being my foot.

I think if you had a camera down there, you'd see it was your foot.

Most often it happens when going for, or resting on the brake, which means you already intend to apply pressure. Perhaps a shoe doesn't give you the feeling that you came down on both.

I would expect if there was a problem, Jaguar would of found it. Its not something they will just not doing anything about if there were a problem.

 

The "Sudden Acceleration" happened to me also, once. Yes, it was because my foot was crooked and across both pedals. The car sped up so I pushed harder on the brake, and the engine raced.
Just like years ago when a whole bunch of old people crashed because of "SA", it was found that their feet were to blame. Since that time I have decided to NOT push both pedals with one foot at the same time, it's never happened again.
Simple error, even simpler fix.

 

I brake with the left, accelerate with the right, so it's harder to get my foot on the wrong pedal. I agree with Teruven & CeeJay, it's most likely to be foot trouble. It's not impossible for the ECM to get a glitched signal that make it think you're booting it, but there are counter-signals that should impede that, like the other signal that says your foot is on the brake.

 

I had my foot on the brake waiting on a stoplight when the car started accelerating. Unless my foot split in half with 1 half flooring the gas pedal and the other half flooring the brake then maybe that could have happened. lol
what if the ecu gets a signal somehow from the gas pedal position sensor to open the throttle or somehow thinks it did.that can cause this sudden acceleration right? does jag ecu stop the throttle from opening if the brake was applied?

 

you think you can floor the gas pedal and the brake pedal at the same time unintentionally in the crooked foot position?

 

There are two sensors, with different characteristics, so no it can't be a bad signal. If one of the sensors were to send a bad signal you get codes / limp mode / etc.

BTW no need to post TWICE https://www.jaguarforums.com/forum/x...-182227/page2/ (OTOH over there you say this has happened to YOU with 2 jags and it seems to me that YOU are the common issue.)

However, what you could have is a sudden air leak so I'd investigate that.

NOTE: your brakes will stop the car even if there were unwanted power from the engine!!

 

Yes, since I did. Once.

 

I experienced unintended acceleration multiple times when I first got my XK.

In all times it was when I took my foot off the throttle pedal, and it kept going with no foot input.

In your case you are describing foot input(foot on brake, which means you may also unknowingly be foot on gas).

The OP also was "slowing down" at the time, describing foot input.

Take your shoes off when driving so you'll have a better feel. I have some stiff climbing shoes that allow me to balance on a marble without touching the ground. I couldn't tell if I was on one pedal or two with those on.

The fact that it surged in RPM as you went deeper on the brake to stop it tells me that it was your foot input on both pedals, more of one, more of the other.

When I experienced a stuck throttle, it was when I took my foot off.

 

I noticed something similar to this today in my Lotus and traced it to the shoes I was wearing. I normally wear a shoe that tends to have a sole that is relatively straight on each side of the foot and never had a problem, but today I was wearing a pair that had a more natural "foot" shape, i.e. much wider in the front/toe box area and then narrowing to support the foot.

It could be that your foot *is* on the brake pedal, but your shoe may also be overlapping the gas pedal. As Tervuren suggests, try driving in socks or find a pair of shoes that closely follow the contour of your foot. That might solve the issue.

 

OK, tested it. The ECU will accept an 'open throttle' instruction from my right foot even when my left is in the brake. So, apologies, I was wrong - you can brake and accelerate at the same time.

 

That is why XK's bring one rear tire in bald when they get to a tire change place.