Hi Guys,

Can anyone provide me with the procedure of how to adjust the TPS correctly?

Thanks in advance!


David
1999 XJ8 4.0

 

throttle position sensor, not sure that one is calibrate-able. What is your concern? Does your pedal position sensor not match your throttle position? Here is the difference in mine from a recent scan.

 

Hi Matt,

I was dumb enough to fiddel around with the TPS setting after cleaning the throttle body and readjusting the throttle cable (got ony 87% throttle per OBD reading).
The TPS can be adjusted (turned). It is mounted with 2 set screws. If you loosen these screws you can turn the sensor.

I played around with the setting because whenever I turn on the ignition the throttle motor is "whining" and with the intake duct removed I noticed that the butterfly was not completely closed.

All in all it was a bad idea as with the engine warmed up I got a "bump" out of the transmission and a very rough engine that fell in limp home mode. Various fault messages appeared (transmission, traction control, restricted performance).

I set the TPS back to normal (luckily there is a drop of color coating on top of the set screws so I could set it as it was before).

Now everything is behaving normal, but I stil have 5% throttle opening + the whining sound of the throttle motor when the ignition is on (no running engine).

Unfortunately my cheap OBD-reader delivers no pedal position readings, only the throttle position.


David

 

In my opinion every thing is fine.
I have always "strange" noice from TPS in Ignition ON.
As I mention before I did supercharged my XK8. Now I have piggy-back integraded. I can make logs. I just checked for you TPS parameters (log before my upgrade).
It looks that before start engine tps was showing 3%~5% being open. After start engine the computer is adjusting TPS and the % value is droping down.

I hope it helped ;-)

 

Thanks Fishman,

the cat indeed baves normal again.
The frighning feeling while driving now still stays though.

Maybe I'll consult a Jag specialist to adjust the TPS properly again.
At least that would help me to sleep better...

David

 

Can you describe this? What exactly is making you concerned?

I would suggest cleaning the MAF sensor, leaving the tps well alone, if you take some time to learn before you leap, hard resetting the car will put the engine into learn mode. This is interesting to watch and listen to as the ecu recalibrates the tps, initially running a high idle of 1500-2000rpm and gradually reduces rpm until almost stall point, once done it's set. A fly-by-wire throttle is not something I'd mess with - adjusting the throttle pedal cable by taking any slack out should be enough.
Saying this, I have no experience of your model year(99) as my cars have the later throttle bodies.

 

Hi Sean,

I'm concerned (almost afraid) that that horrible "bump" somewhere out of the transmission/drivetrain will appear again, along with the engine fail safe mode + all the warning messages.

MAF sensor is new, for the TPS your advice is definitely correct, but in my case too late, I'm afraid.

Could you please explain how to do this "hard reset"?

My XJ has the new version of the throttle body!

BTW - I just made an appointment with Jaguar tomorrow to readjust/calibrate/whatever the TPS as the car still behaves strange.
It feels as there is always some "push" to the pedal. When I approach a red light for example the car will not noticeable slow down.
So I have to use the brakes more and earlier than before my stupid "adjustment". (Idle RPMs are around 750.)
But at least I'm healed from touching the TPS again!

David

 

I wouldn't worry about the bump, if what you did to adust the TPS caused the transmission shift issue, and now its gone after you turned it back, I'd do the hard reset and teach the car to drive again, equal part aggressive, then grandma-mode.

Hard reset is simply pulling the negative terminal cable from the battery, then touching the positive terminal (with all cables still attached). That'll reset the ECM and TCM to baseline and you can teach it. When I do this, I let the car idle for 10 minutes or so to get the base idle point after the computer determines air/fuel mix and such.

 

@Matt, thanks for explaining hard reset to David...

@David, have you pushed the throttle cylinder,(the one the throttle cable wraps round) then released it to see how it returns? it should "thock" back from wide open.....this would indicate it works correctly, if not maybe an issue with the spring, or too tight a turn in the throttle cable, restricting movement? I had carpet leaning on the pedal giving me the same thing rolling up to lights....see if there's something obvious causing this, it would concern anyone.

 

Yes, throttle cable is adjusted correctly. I even keep some slack in it, just to be on the safe side.
There is a plastic pedal stop on the XJ8 (where the kickdown switch on the XJR would be) and I had to screw that plastic part all the way in to get a bit more throttle movement. Full throttle is just about 94 percent though.

As I was wondering...
Can anyone explain to me why the XJ has no kickdown switch at all?

Thanks!


David