I haven't had the engine failsafe message come up for about two weeks. Now I am having a problem with the way the car accelerates.

On normal acceleration, the car drives as it should. On hard acceleration, from a stop, the car takes off just fine, but then starts to jerk, until I back off of the gas. Then it seems to shift properly. Sometimes it feels like the exhaust may be plugged, where the engine is making noise from the intake. This is a real hard problem to describe.

When at highway speed, it will down shift and pass easily without any problem. If it wouldn't perform at highway speeds, I would be looking at a clogged catalytic converter, or dirty injectors, but now I am thinking it may be the throttle position sensor going out.

It is not throwing any engine or transmission codes, or lights, that the Foxwell NT510 can locate........Any ideas would be appreciated.......Thanks.....Mike

 

Check this thread from a few days ago, it may apply.

https://www.jaguarforums.com/forum/x...-power-168159/

 

Sounds exactly like a clogged fuel filter. what do you think.

John

 

Didn't the earlier models have two fuel pumps; would they have two fuel filters as well?

 

They only listed one fuel filter for my car, a 99 XK8, and I changed it. wouldn't a bad fuel pump influence high speed passing? My car flies over 90 mph.

I adjusted the throttle cable, and it helped a lot off the line, but that transition between 2nd, 3rd and 4th gears still has a minor bog. Would the throttle position sensor have anything to do with the way the motor revs and the trans shifts? Sorry for the tunnel vision on the TPS.

The trans has also had the filter changed, and 15 liters flushed through it.....Mike

 

Or a pedal position sensor with a 'dead spot'?

 

Where is the pedal position sensor?....Throttlebody? The bog doesn't happen all the time. That is why I am thinking of something electrical going out...

 

In the Drivers side engine bulkhead cover, I will see if I can find a diagram of the Accelerator Pedal.

This is what I have found so far, in the manual section 310-02.

When the accelerator pedal is pressed, the engine control module (ECM) monitors the angle of the accelerator pedal through the accelerator pedal position (APP) sensor.

For additional information, refer to Section 303-14 Electronic Engine Controls.

The APP sensor is connected to the accelerator pedal through an accelerator cable.

The ECM then provides an output, based on the accelerator pedal position, which drives a DC motor to position the throttle to the required angle. The throttle position is monitored by two sensors for rational value.

The ECM has the necessary safety features to monitor the correct operation of all the components. Depending on the failure state, the ECM can put acceleration control system into an appropriate safe state, from restricting the RPM to limphome mode.

Some Diagnostics from 303-15

Poor driveability Engine hesitates/poor acceleration
Fuel pump
Injector leak
Fuel pressure
Fuel lines
Air leakage
For fuel pump, fuel pressure sensor, fuel line and injector
tests,
REFER to: Fuel Charging and Controls (303-04 Fuel
Charging and Controls, Diagnosis and Testing).
For intake system,
Throttle sensors
Throttle motor
Ignition system
Exhaust gas recirculation
Oxygen sensors
Transmission malfunction
Restricted pedal travel
(carpet, etc)
APP sensor
REFER to: Intake Air Distribution and Filtering (303-12
Intake Air Distribution and Filtering, Diagnosis and
Testing).
For throttle position sensor tests, GO to Pinpoint Test E.
For throttle motor tests, GO to Pinpoint Test X. For ignition
system,
REFER to: Engine Ignition (303-07 Engine Ignition,
Diagnosis and Testing).
For exhaust gas recirculation,
REFER to: Engine Emission Control (303-08 Engine
Emission Control, Diagnosis and Testing).
Check for DTCs relating to Oxygen sensors. Refer to the
DTC index for pinpoint tests for DTC set. For transmission
information,
REFER to: Diagnostic Strategy (307-01 Automatic
Transmission/Transaxle, Diagnosis and Testing).
Check accelerator pedal travel. For APP sensor tests, GO to
Pinpoint Test V. GO to Pinpoint Test W.

Engine backfires
Fuel pump
Fuel lines
Air leakage
MAF sensor
Oxygen sensors
Ignition system
Sticking VCT hub
APP sensor
For fuel pump and lines tests,
REFER to: Fuel Tank and Lines (310-01 Fuel Tank and
Lines, Diagnosis and Testing).
For intake system,
REFER to: Intake Air Distribution and Filtering (303-12
Intake Air Distribution and Filtering, Diagnosis and
Testing).
For MAF sensor tests, GO to Pinpoint Test A. Check for
DTCs relating to Oxygen sensors. Refer to the DTC index
for pinpoint tests for DTC set. For ignition system,
REFER to: Engine Ignition (303-07 Engine Ignition,
Diagnosis and Testing).
For VCT information,
REFER to: Engine (303-01 Engine, Diagnosis and Testing).
For APP sensor tests, GO to Pinpoint Test V. GO to
Pinpoint Test W.

Engine surges
Fuel pump
Fuel lines
MAF sensor
Harness
Throttle sensors
Throttle motor
Ignition system
Check fuel pressure. For fuel line information,
REFER to: Fuel Tank and Lines (310-01 Fuel Tank and
Lines, Diagnosis and Testing).
For MAF sensor, throttle sensor, and throttle motor relay
tests,
REFER to: Electronic Engine Controls (303-14 Electronic
Engine Controls, Diagnosis and Testing).
For ignition system,
REFER to: Engine Ignition (303-07 Engine Ignition,
Diagnosis and Testing).

Engine detonates/knocks KS/circuit malfunction
Fuel pump
Fuel lines
Fuel pressure sensor
MAF sensor
Oxygen sensors
Air leakage
Sticking VCT hub
BARO sensor malfunction
For KS circuit tests, GO to Pinpoint Test O. GO to Pinpoint
Test P. Check fuel pressure. For fuel line information,
REFER to: Fuel Tank and Lines (310-01 Fuel Tank and
Lines, Diagnosis and Testing).
For fuel pressure sensor,
REFER to: Fuel Charging and Controls (303-04 Fuel
Charging and Controls, Diagnosis and Testing).
For MAF sensor tests, GO to Pinpoint Test A. Check for
DTCs relating to Oxygen sensors. Refer to the DTC index
for pinpoint tests for DTC set. For intake system,
REFER to: Intake Air Distribution and Filtering (303-12
Intake Air Distribution and Filtering, Diagnosis and
Testing).
Check DTCs for VCT range/performance fault. For VCT
information,
REFER to: Engine (303-01 Engine, Diagnosis and Testing).
For BARO sensor, contact dealer technical support for
advice on possible ECM failure

No throttle response
APP sensor malfunction
Throttle sensors
Throttle motor
For APP sensor tests, GO to Pinpoint Test V. GO to
Pinpoint Test W. For throttle position sensor tests, GO to
Pinpoint Test E. For throttle motor tests, GO to Pinpoint
Test X.

Cruise control inhibited or disabled
Default mode enabled
Cruise control switch
Throttle sensors
Stop lamp switch
Check message center for default message. For cruise
control switches,
REFER to: Speed Control (310-03 Speed Control, Diagnosis
and Testing).
For throttle position sensor tests, GO to Pinpoint Test E.
Check electrical guides for stop light switch information.

Poor throttle response
APP sensor malfunction
Throttle sensors
Coolant temperature sensor
MAF sensor
Transmission malfunction
Traction control event
Air leakage
Breather system
disconnected/restricted
For APP sensor tests, GO to Pinpoint Test W. GO to
Pinpoint Test V. For throttle position sensor tests, GO to
Pinpoint Test E. For ECT sensor tests, GO to Pinpoint Test
C. For MAF sensor tests, GO to Pinpoint Test A. For
transmission information,
REFER to: Diagnostic Strategy (307-01 Automatic
Transmission/Transaxle, Diagnosis and Testing).
For intake system,
REFER to: Intake Air Distribution and Filtering (303-12
Intake Air Distribution and Filtering, Diagnosis and
Testing).
For breather system information,
REFER to: Engine Emission Control (303-08 Engine
Emission Control, Diagnosis and Testing).

Engine defaults, warning light and messages. Refer to the Driver Information table
Park/Neutral switch
Throttle sensors
MAF sensor
Coolant temperature sensor
Harness
For Park/Neutral tests,
REFER to: External Controls (307-05 Automatic
Transmission/Transaxle External Controls, Diagnosis and
Testing).
For throttle position sensor tests, GO to Pinpoint Test E.
For MAF sensor tests, GO to Pinpoint Test A. For ECT
sensor tests, GO to Pinpoint Test C.

 

Anyhow, the information is from the Owners Manual downloaded from the fifth STICKY down, on the Post Page, titled 'XK8 & XKR 'HOW TO'/DIY Repair & Maintenance Links/Facts & Data'. Hopefully it is this: Restricted pedal travel (carpet, etc), Good Luck.