2003 XJR. After put tank back had P0121 for the first time ever with fail safe warning. Decided to clean throttle body connections with electronic cleaner and add some dialectic grease. Spotted this unconnected vacuum hose. Can’t find where goes.

 

Being it is a crimped clamp, I'd say it was part of the EGR system..like under the purge valve. Should have two lines coming off from under that.

 

You mean EVAP. 2003 XJR does not have EGR. Pic below shows 1 thin line and 2 thick lines going into EVAP.

 

Pic shows where vacuum line comes out under throttle body.

 

Hmmm, have you checked the driver side of the throttle body or a "T" junction back there? This is a replacement sticker from Welsh, I tried blowing it up without distorting it too much.
Other than that, I defer to Addicted or Bob to chime in.

 

MAP sensor. Thanks for the diagram.

 

If you don't have that diagram sticker up by your radiator, here's the link... https://www.welshent.com/Search?k=nnf4744ga

 

Still getting P0121 code. Don't know if unconnected MAP or cleaning connectors had any connection to code. Checked battery. At rest after trying to charge showing under 12 V. Know this cars are sensitive to low voltage. Picking up new battery today.

 

You probably already have this, but here it is anyway. Seems to be a TPS issue...

Just curious, did you put your finger over the hose end with the car running to see if it was drawing vacuum? I wonder if it was disconnected on the other end as well?

Code P0121 Jaguar Description

The P0121 code for Jaguar vehicles indicates an issue with the Throttle/Pedal Position Sensor/Switch 'A' Circuit Range/Performance. This means that the Engine Control Module (ECM) has detected that the signal from the throttle position sensor or pedal position sensor is outside the expected range or not performing as it should. The throttle position sensor (TPS) and pedal position sensor are crucial components that provide input to the ECM to determine the appropriate fuel delivery and ignition timing for optimal engine performance. When this sensor malfunctions, it can lead to a variety of issues affecting the vehicle's drivability and overall performance.

Common Causes of P0121 Jaguar

1. Faulty throttle position sensor
2. Faulty pedal position sensor
3. Wiring or connector issues in the sensor circuit
4. ECM software or hardware issues
5. Throttle body malfunction

Symptoms of P0121 Jaguar

1. Rough idling
2. Hesitation or lack of response when accelerating
3. Engine stalling
4. Reduced fuel efficiency
5. Check Engine Light illuminated

How to Fix P0121 Jaguar

1. Begin by diagnosing the specific cause of the issue using a diagnostic scanner to read the code and pinpoint the faulty sensor or circuit.
2. Inspect the throttle position sensor and pedal position sensor for any signs of damage or wear. Replace any sensors that are found to be faulty.
3. Check the wiring and connectors in the sensor circuit for any breaks, corrosion, or loose connections. Repair or replace any damaged wiring or connectors.
4. Clear the code from the ECM memory using the diagnostic scanner and test drive the vehicle to ensure that the issue has been resolved.
5. If the problem persists, further diagnostic testing may be required to identify any underlying issues with the throttle body or ECM.

 

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Thanks for the info. As to the finger test, I didn't try that but will. Guessing connecting other side of vacuum hose would be a bear. The vacuum hose clamp (the metal snap over ridge kind, what ever those are called) had come undone and would no longer work. Don't know how long it was off. I hadn't done any work in that area it so I know I didn't knock it off. Strange thing after I changed transmission fluid, filter and connector plate and added TransGo kit drove down some back roads for several miles (no tag yet) and it ran great. Now on last few starts, runs fines for a few hundred feet then goes into failsafe and engine runs not rough but with no power. If turn off and on, same thing. When took out battery negative post twisted which can't be good.

 

Jaguar issued a TSB for the DTC P0121.
Your car might be out of VIN range but the info might help?