I'm curious, with my car, a 2003 S Type with the NA 4.2 engine sometimes the throttle response is good, the kickdown works, the car gives a nice roar and goes pretty good. At other times not so much and is kind of sluggish with not much of a roar. At highway speeds the throttle response seems to work better more often than at lower speeds. I've never driven another S Type, so I don't know, is this normal? Does anyone have any tips for getting better and more consistent throttle response and acceleration, etc. Is my throttle not working as normal? Maybe someone has some tricks in applying the throttle to help it? Except for going up and down hills, I prefer to not shift manually for fear it might hurt something. Would an offering help?

 

Could be something else, like an air leak.

Do some OBD work - don't do a codes clear, though! (Unsets OBD monitors and then you can have problems.)

See if you have codes or pending codes (expect P1111, hope not P1000).

Look at OBD live data, especially fuel trims.

 

The car has been like this for years, I just never asked about it before and assumed that it's normal for the car. So this is not normal then? The normal for the car is that the car roars away whenever you give it the gas? There is no check engine light or anything.

 

It doesn't sound normal for a 300HP car, though I really only know the 400HP STR well.

I'd do the OBD things - cheap with such as elm327 but a bit time-consuming.

 

Thanks for replying JagV8. The R model and base model with the NA V8 are probably set up different as far as what normal is. Hopefully someone with a NA V8 will put their two cents in and share some info.

 

Well you could have the throttle readjust itself by clearing the current "memory". But, what about your tranny? Have you ever change the fliud? Mind you I am anything but an expert.

 

pre 06 cars are very sloppy for a number of reasons…transmission tuning and kickdown is one of them

 

Kind of a long shot?
Have you seen this? Might be worth a try as it's zero cost?
I had a 2005 S Type R for a number of years and never did adjust the throttle range and I will say that car had no problems with acceleration!
Throttle Range Calibration
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Thanks for the replies.
My car is a 2003 with the NA V8, so this is pretty normal then? Can the software for the auto transmission be updated? I did have the transmission fluid changed at about 65,000 miles and it's clean with no leaks. I kind of figured that the transmission has to give the engine permission to crank it up and is kind of moody.
What do you mean by clearing the current "memory"? Does this mean disconnecting negative lead on the battery and doing the "throttle range calibration" after reconnecting or just doing "the throttle range calibration"?
Does anyone have any tricks for applying the throttle?

 

Battery off clears little, mainly learned values like fuel trims and throttle pedal min/max - things you don't normally want to lose. No effect on gearbox (need IDS/SDD for that).

Throttle (re)calibration can't hurt bit don't get your hopes up. (I wouldn't bother doing it.)

Battery off will reset things you probably want to keep like used for smog and to be able to report faults (DTCs). Those will be suppressed unless the values are relearned OK.

 

Thanks for all the feedback, so I guess the performance of my car is pretty normal. Maybe I'll see if a Jaguar shop can update the software for the transmission or give me advice on a proper offering or ritual that I could do.