Greetings to all...........Hope some forum members have an answer to my problem. I have a 2007 XK, that on several occasions, has had sudden acceleration issues. Problem has shown up while driving at very slow speeds. Luckily I was able to stop the car and turn it off, however when trying to restart it will not, wait for 15 min. and it restarts and shows no issues, no dash lights etc.

Thanks for any and all help. Be safe.

 

The most likely is probably an air leak. In effect it's like you put your foot on the gas.

There are many threads about hunting for air leaks.

 

I doubt its an air leak, acceleration requires both fuel and air.
Unintended acceleration is impossible in modern cars, the TPS has 3 sensors in it, 2 reading voltage 0-5v and one reading voltage 5-0v. If any of these fail to agree the computer will idle the engine. Acceleration can only occur by throttle action.
I wonder if you have a cruise control issue, could the 'Resume' function be engaging?
Regards,

 

It could be an air leak, could be a dirty maf.

The clue is he says it happens when he puts load on the engine or mimics a stalling engine when driving at slow speeds. The computer compensates by increasing fuel, to air it hasnt metered.

But then again, wouldn't unmetered air throw a code?

I have an intake manifold leak on a domestic car, it does the exact same thing. But it does throw the code for fuel injector bank 1 and 2 being too lean.

 

If there's extra air the PCM will add fuel to try to match it, so it's not impossible.

That said, more data would be useful. The car can easily be monitored (OBD live data) during normal and abnormal behaviour.

A code might or might not result - but such as lean codes need 2 occurrences and under near identical conditions. Before then you'd get a pending code (which some tools do not report). Worth checking for.

 

The next time you can't start the car, pull back on the throttle pedal from underneath to make sure it isn't engaged.

Could something be sticking/catching the throttle, floor mat perhaps?

 

Not much of an original post to troubleshoot from so everyone is shotgunning. Define slow? Is the car warm or cold? Exactly when does it do it? Can you define the moment ex, cold drive away within a minute of startup? Or warm idle at a stop light with brakes barely on?

A better and more descriptive description of the problem you give will net a far more concise answer. Could be something as dumb as your foot hitting the go pedal at the same time as the stop pedal.

 

Mine does he same thing but it only happens as I am approaching a yellow traffic light

 

+1

 

Well trained cats.

 

Thanks to all who have taken the time to answer. To be more precise it happens when the car is warm and at very slow speeds. It happened once when I was pulling into the garage (that was super scary as I was almost fully into the garage), I believe I had my foot on the brake. Second time I was pulling into a parking spot at very slow speed. Car has been perfect for the 3 yrs I've owned it with this problem just starting to occur.

There is no physical link between the gas pedal and the intake, it's signal controlled. This problem has stumped a very smart Jag mechanic. The problem cannot be reproduced so it's very hard to diagnose. One educated guess was a faulty potentiometer which reads pedal position.

Once again thanks for all the input so please keep it coming. The car is currently back in the shop. I will keep all informed if and when I find the problem.

 

The engine is not stronger than the brake. Usually this happens when somehow the accel pedal has been pressed, such as by the side of a shoe or a mat.

 

Has it been doing anything else unusual? Sounds almost like a battery related communication bus issue or a ground issue. Gonna be almost impossible to duplicate so it's important that you remember what was happening when it lost it's mind and tried to take off.

 

JagV8 has hinted, as did I in an earlier post about the real cause of unintended acceleration which was an issue some years ago in the U.S. at least, and perhaps elsewhere.

In the final analysis was it was discovered the driver, who inspite of his/her insistence they did not, did in fact press the accelerator pedal instead of the brake pedal as they believed. The consequences of this were sometimes tragic.

The drivers involved were absolutely convinced they had pressed the brake pedal instead of the accelerator, and could not understand why the engine accelerated at the same time the brakes failed. Even very experienced drivers were surprised to be caught out by this, and this is why the TPS is now such a sophisticated device.
Unintended acceleration cannot happen, period.
The fix was to move the pedals futher apart.
Regards,

 

I have also experienced unintended acceleration, and it didn't take long for me to realize that it was my fault.

My running shoes have a much wider sole than my dress shoes, and inadvertently depressing the corner of the brake pedal also occasionally makes contact with the gas pedal. I now make a conscious effort to step on the center of the brake pedal.

The larger your shoe, the more likely this can happen.

 

Thanks to all for further input. I can say without reservation that the sudden acceleration was dramatic !!!! I repeat dramatic. The RPMS must have gone to 5k which would have meant that I would have had to smash the accelerator and I can guarantee you that did not happen. Keep the input coming.

 

An air leak won't do that.

Something pressed the accel pedal.

 

....or, "sensing" the accel pedal is depressed?

 

Definitely sounds like you have an object sticking your pedal, be it floor mat or your foot.

The electrical design of throttle by wire causes throttle cut out in the case of faults, not a WOT signal.

A surge like that is most likely to be physical application. Especially if Jaguar looked at it and didn't find any faults.

 

To get a second opinion of the problem, you could swap cars with a friend or relative for a couple weeks to see if they experience it. If its a friend, warn them about the issue you've experienced, and to look out for it. If its a relative you're not crazy about, skip the warning...