Car accelerates on its own

For about six years, my car has had a problem with accelerating on its own. At first, it was really bad, with the engine running at maybe 2800 rpm's when I was trying to go about twenty mph.

I have had it to various Jaguar dealerships during this period, and they have tried all sorts of things (including changing the thermostat, cleaning and lubricating linkages and throttle cables, checking the throttle return spring, replacing the battery, various adjustments). I cannot recall everything they have tried, but the problems still persists, although it is somewhat better. Now, if I am going down the road, it will gradually accelerate (for example, from forty to fifty plus mph). I can brake and slow it down, but then it will start accelerating again.

I have had it at the dealership for months as they try to diagnose and fix it, but they have had no luck. I also called Jaguar North America, so they are somewhat involved, too, but their experts do not seem to be able to advise on this.

I also recently went onto the internet to investigate the problem, typing "1996 XJS accelerates on its own", and it appears that this is not a totally rare problem and certainly not isolated to my car. Many Jaguars suffer from the same condition (XJ6s, x-types, XKs, etc.), But so do models by other manufacturers such as Jeep, Chrysler, and Toyota, to name a few.

Have you ever encountered such a problem, and if so, how did you resolve it, if you were able to? It can certainly be quite dangerous. I think it must be something that later models have done that did not exist in earlier models, and I think one solution would be to trace this back to the earliest occurrences and then see what the manufacturers did differently than they had in previous years.

As another note, upon reading on the internet, most times the dealers would just say it was driver error (e.G, you must have stepped on both the brake and accelerator at the same time), but at least the Jaguar dealerships have acknowledged the problem on my car exists. They just have not been able to fix it.