car goes to failsafe
 

If i'm driving down the hyway for awhile and at a constant speed usually on cruise and I take it off and accellorate, car seems to miss and goes into fail safe mode. Brought it into the dealer and code P1121 came up. (pedal demand sensor A circuit range/performance) then a pile of BS. Does not seem to do it if the cruise is not used. Any thoughts

The Cruise Control is designed to allow you to apply the accelerator without turning off the Cruise Control. The display will read back CC Override until you are done accelerating and either set a new speed, or allow the vehicle to resume it's previous speed; it will 'time out' if you are using the accelerator too much and discontinue the CC automatically. Since the accelerator is 'fly by wire', and the CC electronics take control of this when activated, there could be some confusion if the CC is Cancelled, and the accelerator immediately applied, perhaps something unexpected to the CC electronics, instead of just applying the accelerator and using the 'built-in' Override Function to accelerate at will, as I assume you are cancelling the CC, then accelerating full on? If this is the case, perhaps the CC electronics do not have enough time to release the accelerator back to manual operation, and you hit this conflict, related to the pedal sensor as you stated 'P1121 came up. (pedal demand sensor A circuit range/performance) then a pile of BS'. Also, please post the pile of BS, as it may be meaningful to someone on the forum to help diagnose if this is actually a problem, or a conflict in the control systems due to the rapid change of state, from running on CC to full on manual accelerator operation.

Just did a quick search for P1121 and it appears to relate to the TPS, or Throttle Position Sensor. It could be out of adjustment or just on it's way out, but there are tonnes of posts related to removal and replacement. Check this post: https://www.jaguarforums.com/forum/x...ighlight=P1121