I wish these cars were better about throwing codes.....

 

Hi there, XJRGUY -
I'm in Providence, RI and I have a '96 4.0 X300 , not an R, though.
Any idea how I can locate an independent Jag guy who can do the throttle adaptation reset, oxy sensor orientation and the resetting the ECM adaptations.
There must be someone around here that works on these cars.
Is there a secret society or do I just have to ask around.
I know from having a 1970 BMW R75/5 bike that the dealership didn't want to touch something old
that's gonna be a minefield of un-foreseeable issues that the customer probably can't afford.
I found that guy back then in San Francisco and he was great.
25 years later on the East Coast and a Jaguar, not a BMer, but there's got to be that guy.

Any tips would be great.
Thanks,
J. Shelter

 

Jaguar dealer should be able to perform a TPS Reset for you. They should still have that capability.

They should also be able to do an oxygen sensor reorientation, but it really shouldn't be necessary, unless you've swapped oxygen sensors and forgot what was what.

They won't be able to perform the base idle reset, since you need a PDU to do that, but I have one and I'm not sure it was really helpful in solving anything. It just resets the long term fuel adaptations, most likely to aid in diagnosing whether a recent repair or sensor replacement was able to resolve a fueling issue.

There are other third party software packages that will do the same, I believe the AutoEnginuity system has the capability to do this.

You can also buy a MongoosePro and do it. They sell knockoffs for a lot less, but they may not last too long.

 

The TPS is the only item in this discussion that requires adaptation to be done. Everything else the car will adapt in its own. You can clear all systems memories by disconnecting the battery cables and touching them together to completely reset everything. Then as you drive the car will relearn the limits and trims which are learnable.

 

Contrary to what I accept is the established "official" advice, I fitted a new TPS to my XJR and it worked straight out of the box without adaptation. I took care to make sure the battery was disconnected from start to finish of the work, but am not sure that this was necessary. There may be minor differences between sensors, but for something as relatively uncomplicated as a TPS, it shouldnt be material to the signal provided to the ECU. My car drives normally, and idles beautifully.
Finding someone who can perform the adaptation is becoming increasingly difficult, and if you need a new TPS, I would suggest fitting it and seeing whether you are happy with the result. I am pretty sure it will be a huge improvement on the 900/1100 rpm tickover even without adaptation.

 

A new TPS doesn't always mean you need a reset.

As your engine gets older, the car learns and adapts to the changes in tolerances. This, over time could require that the car adapts to different fueling requirements over time. If that happens, and you replace the TPS, then a reset could be required. If the butterfly gets completely layered in oily soot, and you leave it that way for a long time, you might also find that a TPS reset may be required when you clean out the throttle body, but leave the TPS in place.

It's not an "always" situation, but it certainly is a common solution. The advice is in response to an "if" situation. IF you replace your TPS, THEN your idle is high, a reset is advisable. IF you clean out your throttle body, and leave or renew the TPS, THEN your idle is high, a reset is advisable. IF you do do either of the two, it is always possible that you return to a solid idle.

 

The AJ16 in the AJ16 will NOT clear LTFT by disconnecting the power, or touching the posts together. I'm not sure that does anything at all to the AJ16 in any model car. The LTFT requires a PDU to reset it. I'm not aware of any other method, and it's been discussed for decades here. Don't believe me? Do a search. It will absolutely NOT clear all systems memories, so do not subscribe to this statement.

Will it clear the common P codes, possibly, but you can also do it with any $10 OBD2 reader. What about reset Transmission or ABS codes? Not sure. I've never tried it. You will need a diagnostic device specifically programmed with Jaguar software to pull those codes.

 

Aren’t all adaptations stored in NVRAM and if so what happens when you remove its backup power source or just run out the clock?

 

You've been just lucky but we don't necessary need to rely on luck here. TPS basically operates within ~0.6V to ~5V range. The lower end value is key when it comes to idle. Lets say ECU has learnt that your base idle TPS voltage over the years is 0.61V-0.63V with a closed throttle body and that is exactly what is has stored in memory. Anything over(more than 0.02V) that voltage will cause high rpm idle.
You changed the TPS and if you fitted it, in exactly the same position as the old one it should also give 0.61V to 0.63V at closed TB and foot off the pedal. Contrary to what it may look like, there is enough slack in the TPS bolts to adjust/change that voltage by 0.12V so you could have putted it back together and it would show 0.7V with closed TB and foot off the pedal. Because ECU has stored eg 0.61V as base idle TPS voltage it would think that you actually have your foot on the gas pedal, it then retracts IACV and you get extra air in the system, extra fuel and high rpm idle.

So the key to successfully swapping TPS without need for TPS adaptation is to first check that base idle voltage BEFORE you swap the TPS, when the car actually idles ok and then making sure that the new TPS goes in exact same position and gives you exact same base TPS voltage. This voltage can be checked through OBD with the engine on or off. OBD scanners might show TPS voltage in %, eg 11.37% but easy to convert it to V or just use %.

Its also a good idea to check TPS operating range, the closer it is to 5V or 100% in OBD at wide open throttle(basically foot fully down) the better. This is the only way to get correct fuelling and full BHP out of your engine. Because cable stretches over time the TPS can often show as little as 4V at WOT and car can feel very sluggish, adjusting it to closer to 5V or 100% can often feel like adding an extra cylinder to the engine.

TPS adaptation is therefore mainly needed if the base idle voltage is quite out of its normal range, eg 0.4V or 0.8V, if its around its normal operating range which is 0.6V or 12% you can certainly get by without doing it. Hope that makes sense.

 

if you Google what NVRAM is, this is the first thing you will see:

Non-volatile random-access memory(NVRAM) is random-access memory that retains data without applied power.

 

NVRAM often means SRAM with a battery backup, like for example the external 2032 battery that retains bios settings on a PC. If it’s early flash memory (EEPROM) then you can’t wait out the clock, they retain data for decades.

 

Katar,
I understand the point you are making, but of course one problem is being able to determine the "correct" idle voltage once your TPS has become defective and the idle is too high: you no longer have the correct reference point. I may well have been lucky, but I suspect also that modern manufacturing techniques are able to turn out TPS which are extremely close to specification, and are effectively the same. I was also careful to take up the almost imperceptible slack in the mounting screws to give the "lower" voltage at idle.
As an aside on this topic, my friendly main dealer is no longer able to get the latest version of the factory diagnostic software to communicate with my car, so hopes of adaptation at the dealers may be vanishing.

 

I guess in this instance, NVRAM, actually means NVRAM, because that's what it is. There's no lithium battery.

 

I don't think you understand what is going on here. The TPS is perfectly fine, and has nothing to do with manufacturing it within specification. I'm sure it's perfect.

Its the ECU that has adapted itself to expect a slightly different voltage at idle. Now you are introducing a perfect TPS, and the base idle no longer matches what the ECU is expecting, since it has learned that it should expect a less perfect voltage. That's the whole reason behind "resetting the TPS" through the PDU, WDS, etc. The device resets the ECU's expectation for base idle, it doesn't do anything to the TPS.

Make sense?

 

Katar,
I think I do understand what is going on.
The TPS is a variable resistor, or rheostat. Its function is to convert the movement of the throttle pedal into a correspondingly variable signal voltage to the ECU to allow it to respond to the drivers intentions. The TPS is a moving part, and like all moving parts, eventually wears out. The wear is concentrated on the part where there has been most contact between the moving surfaces, ie the part at and near idle. As the wear reaches its advanced stages, the signal voltage to the ECU moves from its intended level, or may disappear entirely, causing the ECU to produce a different Idle level, based either on the revised voltage level or by reverting to a default table in the absence of a signal.
The ECU is not self learning or adaptive in this regard, and the expected voltage values remain fixed, and the only way a 650rpm idle will be achieved is if the correct voltage signal is received by the ECU.
When I fitted my new TPS, at the Idle position, and thanks to the accuracy of modern manufacturing techniques (and the absence of Lucas!!), it produced the correct Idle voltage signal. My ECU had never been altered and obliged by producing the corresponding 650rpm idle.
It may indeed also have just been luck, but the above explanation works for me. I suspect the adaption process is a throwback to the AJ6 and more Lucas infested engine bays.

 

When the TPS wears out, you'll know, because it won't affect your idle....your engine will shut down...while you're driving...even at high speeds! As soon as the TPS sends a dead signal, the engine turns off and your dash will hopefully flash some codes, but it won't give you a TPS related code. It'll be some misfires, a transmission light will come up, etc. Anything but the TPS code.

The ECU does learn, and is indeed adaptive regarding the TPS. In fact the manual says, "The model CTS 518 throttle position sensor is a nonadjustable single-track potentiometer connected to the spindle on the throttle shaft. The ECM adapts to the TPS idle position to compensate for aging and component wear."

 

Vee,
When I first read your reply, I was rather puzzled, as You seemed to be saying that TPS wear causes total power loss, not idle issues, and that the ECU can adapt to changing TPS inputs to maintain the originally intended idle speed. Surely if that were so, TPS wouldnt be one of the principal culprits for idle speed woes?

As I read your post again, It seems that there are two points on which we seem not to agree.
Firstly, when I used the expression "worn out" in relation to the TPS, I was referring to the point at which it no longer performed as per original specification, not when it ceases to function entirely. Real world Failure mode for a TPS is not total loss of signal hence total loss of power / engine shutdown would take a very long time to emerge, not least as most of the resistor track is hardly worn. It is the part at idle which tends to fail first, as, obviously, it experiences most wear, producing a distorted output which causes the ECU to command a higher idle speed.

As for the ECU being adaptive, I am not sure that we are saying different things. The ECU is inherently and continuously adaptive, in that it uses a variety of input data and seeks to produce similar outcomes across a wide range of different conditions and scenarios. As the engine and components wear, the ECU may need to use different settings from those it has used historically to produce any particular outcome. I dont think we disagree on this. Where we do differ is in relation to what the ECU can adapt to. The TPS is a source of input data, and indeed the only source of data relating to the throttle position. The ECU has no means to know whether a reading of , say, 6.9 volts is due to wear on the TPS or the driver having the throttle slightly open. What it can "know" is that, say, the amount of fuel required or the ignition timing required to produce a particular rpm (all other things being equal) has changed over time due to wear and tear. So exactly as the manual says, the ECU does indeed "adapt to the TPS idle position to compensate for aging and component wear". That is NOT the same as adapting the TPS idle position reading. The ECU works on the basis that the input from the TPS is correct, as I believe it does for all of its primary sensors.
Put another way, if what you are saying is correct, and the ECU could adapt for wear on the TPS, why would there be a need to change it on cars with high idle but which otherwise drive perfectly well?

 

You don't. Jaguar claims that a reset is not mandatory, and that, over time, the TPS should adjust back to a normal idle. It never says how much time, and I've never been patient enough to want to find out. Resetting it simply fast forwards through the relearning process.

I'm not sure how a resistor track gets to be worn. I know over time, the friction will wear away at the track, eventually leaving a "bare spot". That would be total failure, and a symptom of that is engine shut down. I'd like to learn more about other ways to wear down the track. I figured there's either metal there, or there isn't. Maybe partial metal is gone? How does the metal track wear such that the reading is distorted?

My point is wholly with the butterfly and, how over time, tiny fractions of an inch are taken away by buildup and grime such that the butterfly, when closed, is no longer at .002", it is now at .00237". At .002", out from the factory, that is read by the TPS as .60v. Now, over time, that butterfly cannot close all the way back to .002", only .00237". That is read by the TPS as .064v, which the EXI has adapted as the idle baseline.

Now, someone goes in and cleans up the throttle body and refits the same TPS, or a new TPS. The ECU was no longer expecting a voltage reading of .060v, (or maybe even .057v) and will idle higher than normal. You can either reset the TPS, so that the car skips the learning process, or adjust the TPS so that at closed butterfly, the TPS rests at .063v, and you won't have a problem. Or....you can wait for the car to learn this itself.

The bottom line is that the TPS reset never appears to be mandatory, but I just don't know how long it would take the ECU to relearn the new idle reading. It's certainly not a couple of days of driving.

 

A great debate here, all I would contribute is my recent following experience -
whilst my car retains its original TPS, idle speed has fluctuated at times over the yrs. A good run, readjustment of the throttle cables or a throttle body clean up & adjustment of the throttle plate clearance usually worked.
As I previously mentioned I recently had to complete “02 sensor orientation” ( car locked into open loop)
Following this, whilst ok, idle speed was not really to my expectations so I decided to then do TPS adaption.
The Legacy/IDS screen asked “had TPS been replaced - yes or no”. If one ticked no it went no further, however when I ticked yes it proceeded to test, which was very quick & said “passed”
Result - idle speed spot on recommendation, perfect.
As with must Jag info, some of their publications (official) advise test if throttle body is cleaned or any work done in that area. That is of course contrary as to what comes up on the Legacy/IDS screen, which completes test only when you tick that a new one has been installed.
Obviously a worthwhile test, especially when we are looking at 20/24 yr old vehicles which we would like to keep running as they were designed to run.

John Herbert
(1996 XJR - 184000klm)

 

Vee,
I agree with everything you say about the ECU adapting to general component wear, and agree that throttle butterfly spindle wear would be included in this. We also agree that a TPS adaptation procedure isnt mandatory, and it is worth fitting the TPS and trying it out first.
As for how a resistor track gets worn, it is perfectly simple. An "arm" connected to the throttle cable / spindle wipes across the tracks of the resistor to produce the variable voltage to the ECU, The physical contact between the arm and the track involves friction and wear, and as the surfaces become thinner, the quality of the contact between them begins to deteriorate. Add in any oxidisation which may occur, or contaminants which may enter as the TPS plastic spindle wears and you have a scenario where the output readings produced while the arm is in the worn sector begin to deviate from specification, likely leading eventually to complete loss of signal. The high idle fun and games seem to arise before it gets to that point of total failure.
In the depths of my despair that my car might never idle properly again, I was interested in some of the threads in the forum about whether the TPS was in fact a FORD part and could be sourced much more cheaply than the OEM sensor. There was not a definitive answer posted by anyone who had actually fitted a Ford part successfully, so I chickened out and bought OEM, not least as it is such a pain to fit the TPS to the supercharged throttle body, and I didnt want to do it twice!