12.11 - Fuel Fail 11, idle trip signal out of range ( Brett Gadzinsky,  )

Fuel fail 11 is for the idle trip signal out of range. It has nothing to do with the throttle or the throttle position sensor.

The idle trim signal is built into the MAF (Mass Air Flow sensor). It is used to set the base idle mixture before oxy sensor correction. Normal output signal is about 2.5 volts and does not vary. Its set at the factory, and never needs adjustment.

It was used up to 1993 year cars, then Jaguar used an adaptive system.

The actual adjustment pot is built in the maf sensor, but is not really part of it, that's just where Jaguar (or bosch) stuck it. Since you cant get at it, its behind a sealed plug, it cant really go wrong, and your problem is likely from a dirty connection on the maf sensor.

The maf sensor is critical on how the engine runs, and its connections are sometimes abused by the connector hitting the coolant tank, make sure the connector is clean and tight. The first step would be to clean the connector using contact cleaner or WD40 , and then add a dab of dielectric grease to the contacts before reassembling. The parts stores sell the grease. You may have to disconnect the battery or pull the ECU fuse to clear the code.

If this doesn't fix it, the throttle pot itself may have failed. Cleaning the throttle body with solvent and getting it in the throttle pot can cause it to fail. The check procedure is nicely described in Haynes.