1996 Jag xjs -when I start the engine, it accelerates without touching the gas pedal, and will continue to do so until I brake. I buzz down hwys without ever touching the gas pedal. I've had the cables replaced but it still acts like it is set on cruise control.

Ford products had a recall because of run away ECM units
as to hard brake pedal , that is because there is no booster to assist the brake action
I suggest that you trailer it to a ford dealer ship and leave it there until it is fixed
call ford technical department and report the occurrence
there may be an explanation if you have the fault codes read

Clutch plate and pressure plate seem to be too weak to pull the car. To test the clutch plate, park the car on flat surface. Pull the hand brake up, start the car, depress the foot brake pedal, depress the clutch pedal, put the car in 1st gear, press the gas pedal and leave the clutch pedal at once, while keeping the brake pedal depressed.
Follow one of the two following statements:
1. Engine does not shut down and remain start. (Clutch plate, pressure plate and clutch bearing defective - Replace all as a set)
2. Engine shuts down. (Clutch system is OK and does not require any repair).

Replace Fuel Pump .

Check the help links related to this problem.Click the link below to go through its troubleshooting procedure :-----Idles rough and quits when gas pedal is pressed less? http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html---------
Car won't start without hitting the gas pedal? http://schematicsdiagram.blogspot.com/2011/12/car-wont-start-without-hitting-gas.html
-------Complete loss of brake pedal then all gets normal? http://repairhelpcenter.blogspot.com/2012/01/complete-loss-of-brake-pedal-then-all.html
------Car dies when gas pedal is pressed? http://schematicsdiagram.blogspot.com/2011/12/car-dies-when-gas-pedal-is-pressed.html
--------Pushing on the gas pedal, but the car slows down? Gas pedal to the floor and the car slows down?

http://technoanswers.blogspot.in/2012/02/pushing-on-gas-pedal-but-car-slows-down.html

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After replacing brake rotors and pads, brake pedal remains on floor? http://technoanswers.blogspot.in/2012/02/after-replacing-brake-rotors-and-pads.html

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accelerator pedal sensor? http://technoanswers.blogspot.in/2012/02/2009-chevy-impala-accelerator-pedal.html

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For rough idle issues and problem troubleshooting,go through the help links provided below :----- van idles rough?

http://howtobyme.blogspot.in/2012/01/2004-ford-freestar-van-idles-rough.html

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will not idle when cold?

http://technoanswers.blogspot.in/2012/02/ford-explorer-40-will-not-idle-when.html

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runs lean and idles rough?

http://technoanswers.blogspot.in/2012/02/ford-runs-lean-and-idles-rough.html

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Engine stumbles coming off idle when warm?

http://repairhelpcenter.blogspot.com/2012/01/engine-stumbles-coming-off-idle-when.html

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Erratic idle on car?

http://schematicsdiagram.blogspot.com/2011/12/erratic-idle-on-car.html

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Low idle when cold out side?

http://repairhelpcenter.blogspot.com/2011/12/low-idle-when-cold-out-side.html

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Idle Air Control (IAC) Valve Replacing?

http://schematicsdiagram.blogspot.com/2011/12/gmc-idle-air-control-iac-valve.html

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Engine quits at idle?

http://repairhelpcenter.blogspot.com/2011/10/engine-quits-at-idle.html

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Car overheats and Air blows hot at idle?

http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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This will help.

Thanks.

For this types of problem,there are few help links.I suggest you to click the link below and go through the troubleshooting procedure :-----Car only starts when gas pedal is pressed? http://technoanswers.blogspot.com/2012/01/car-only-starts-when-gas-pedal-is.html-----------Car won't start without hitting the gas pedal? http://schematicsdiagram.blogspot.com/2011/12/car-wont-start-without-hitting-gas.html
----------Complete loss of brake pedal then all gets normal? http://repairhelpcenter.blogspot.com/2012/01/complete-loss-of-brake-pedal-then-all.html
----------Car dies when gas pedal is pressed? http://schematicsdiagram.blogspot.com/2011/12/car-dies-when-gas-pedal-is-pressed.html
--------------Pushing on the gas pedal, but the car slows down? Gas pedal to the floor and the car slows down? http://technoanswers.blogspot.in/2012/02/pushing-on-gas-pedal-but-car-slows-down.html
-------------Idles rough and quits when gas pedal is pressed less? http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html----------This will help.Thanks.

possible vaccum line problem and when you hit the brake your brake booster is changing the vaccum pressure idling your engine up

down the dipstick tube!!!(really)DO NOT OVERFILL...
Your audi is fitted with a fuzzy logic gearbox, it will change according to your driving style.TRY THIS,put into 1st and without touching gas pedal, let the car accelerate to top gear,stop Then using onle 1/3rd gas pedal do it again.then using 2/3rds do it again.then only using the minimum pedal req accelerate to max legal limit.(try not to use brake pedal,let the car slow down itself,until you have to)then drive as normal, it will feel like a different car.

where does the noise come from? engine? back of car? can you feel it in the steering wheel? more through the brake pedal? is it worse under heavy braking? does it change when you brake or accelerate harshly?

I would replace the crank shaft sensor on the front of the engine.