I'd like to point out here that there is enough slack in original TPS holes to change the rest/idle TPS voltage by 0.06/0.08V, enough difference to cause 2000 RPM idle in more extreme cases, TPS looks like its completely not adjustable but its far from truth, I've checked on multiple cars while cleaning TB, its not difficult with an OBD reader plugged in and intake plastics off

Breaking TPS signal on a failing TPS will never cause high idle, it will cause stalling and idle fluctuations.

As Parker rightly said, high idle will only be caused by mismatch of idle TPS voltage and what is stored as idle TPS voltage in ECU. Any difference over 0.02V will cause high idle, anything under 0.7V can be generally dealt with without adaptation, anything over that and its probably best to look for replacement ECU as its pretty much impossible to find someone with a PDU, at least in UK.

 

The slight adjustment of the TPS without removing the TB takes some patients to reach under there upside down and not everyone has small enough hands

If I recall it is a 6 point torque bit of a certain size to save some frustration in the heat of battle

 

f the microscopic movement of the TPS within the attachment lugs can generate an incremental 1350 rpm as you suggest, how come the entire range of the TPS movement generates proportionately so much less? Put another way, if a few degrees of movement gets you to 2000 rpm, why does the rest of the 90 degrees of TPS movement produce proportionately so much less? Were any of the cars you worked on supercharged?

 

It will if that is what the ECU is programmed to do in the absence of a valid signal....

 

Fitting an OEM replacement TPS will bring any difference within tolerance for the ECU to "learn" , in other words restoring normal idle. How on earth do you imagine that a replacement ECU will fare any better than the existing ECU when confronted with the wrong signal from the TPS?

 

its the luck of the draw if you obtain a replacement TPS when mounted if it matches the ECU orientation or it's told to null point on day one of engine restart

the TPS sensor mounting holes are plastic on the TPS and can be drilled up a size to get you more adjustment.

I can remove one for you from a X300 fresh arrival to a salvage yard i go to

cheaper than a ECU

Have you done a ECU connector inspection?

I my opinion and I can be wrong the TPS once reaching the idle voltage value triggers ( and the key word is triggers ) the ECU to regulate the engine in a idle mode with set perameters

If one of the parameters is to do what ever it takes to maintain the correct idle speed it would not be the case

But at idle the ECU brings the IAC to the idle opening gap , closes the EVAP valve , closes the EGR valve , and maybe starting up the smog pump run cycle again

 

Which it isn't. Car will die.... A TPS with "dead spots" will wreak havoc on your ability to drive the car safely.

 

Replacement ECU may have been removed from the car when the TPS tolerance was anywhere between 0-7 degrees maybe?

 

I don't think smog pump ever runs again after startup. I could be wrong, but I'd like to see that first.

I believe the smog pump is activated solely upon startup of the car and that's it.

 

Countyjag,

I think if you were to do some research on how the the TPS works and how the ECU reads it, you would understand the relationship they have. There are some manuals at jagrepair.com that would help.

Basically the ECU is designed to expect a certain reading from the TPS upon startup/at idle. The ECU has been programmed to slowly adapt to aging throttle bodies over time and relearn new base idle positions of the TPS as the butterfly cannot close back to it's original, fresh from the factory position. When the TPS is so filthy, or when drastic changes are made, it is no longer in sync with what the ECU has learned, or become accostomed to. A reset via PDU or WDS will allow the ECU to renew it's expectation on where the TPS should be at idle. Simply replacing a TPS cannot restore that expectation since it isn't malfunctioning, it has simply shifted its range based on dirt and age of the throttle body.

A TPS with a dead spot is something else entirely and is not a commonly reported problem.

 

Its nothing unusual, its how the fuelling map is set up in ECU. Same issue happens and its easier to explain at the other end of TPS travel at around 5V, very often due to throttle cable stretching over the years max tps voltage with the foot down only gets to around 4V and at that voltage car even though revs normally feels like a 5 cylinder car hence why its so important to check TPS travel with an OBD scanner. The closer it is to 5V the better performance you get. I've never worked on SC car TB but there is nothing different to NA cars when it comes to TPS and how it works. The only difference is a fuel map in the ECU.

Vee is correct. ECU isn't programmed to do this, you can check it yourself by simply disconnecting the TPS while car is running and it will die immediately.

No it wont, it fully depends on how you screw it in. if old TPS at idle was showing 0.66V(and that's the value stored in ECU) and you put new one in and set it to 0.7V at startup, you're going to have high rpm idle. Many years ago, when I still didn't know how this works I was driving for a full month with high idle rpms and probably done well over 1k miles at the time and ECU still didn't adapt to new TPS idle voltage so although we all know that this happens noone seem to know how the relearning actually works or how long it takes.

As for replacement ECU, if your existing one has an idle TPS voltage way over 0.7, its easier to find an ECU with a TPS voltage closer to factory 0.6, you could even get a matching set of ECU and a TB with a TPS still attached, at least in UK it would be cheaper than a new TPS or a visit to a Jag dealers to try and get an adaptation done

 

Gentlemen,
It seems we are destined not to agree on the workings of the TPS and its relationship to the ECU, but as, after a long and frustrating saga, I have successfully restored the correct level of idle on my car I am content to rest on my laurels so to speak….
My original purpose in responding to the thread was to offer assistance to a forum member who was seeking it. In particular I wanted to debunk the old wife’s tale about new TPS not working without adaptation, ( which for many members is basically unobtainable) in which endeavour I seem to have succeeded.
By all means enlarge the holes on your TPS if that floats your boat, or play ECU swap lottery in the hope that you find an ECU which solves your problem. ( owners of supercharged cars should ignore this paragraph, since neither of these things is happening on planet earth anytime soon) but there is no getting away from the fact that if your TPS is worn to the point your car has a high idle, you likely need a new one. I know they are ridiculously expensive for what they are, but a couple of hundred pounds in the context of current world car ownership costs is not excessive.
Caveat emptor when you eventually encounter high idle and are reading all of this!

 

As can be seen in another thread, i am suffering a high idle and have tried everything, cleaning the tb, replacing coolant sensors, replacing thermostat, iacv etc etc, and have not found a solution.
i ammleft at this point with the assumption that the TPS is either in need of calibrating or replacement.
given it is 365000km on the car, who knows it could be everything wrong. Lol.

i have it booked into a jag specialist (who drives one himself and has done a full rebuild) on 22nd feb. This guy knows the cars very very well and should be the one to sort the issue for me.

i will most definitely report back after my cat has been to the doctor.

 

Why not simply read from the various manuals issued by Jaguar about how the TPS works and it's relationship to the ECU?

jagrepair stores many useful files for download!

I've attached a training manual if you'd like to look through that as well?

Spud Maat, I'm looking forward to hearing how your issue will be resolved. I am always interested in hearing about this common issue and how it is resolved.

 

Vee,
There is an assumption in your recent remarks, and this one particularly, that I am somehow less equipped to comment on this subject than you. I am sorry that my contributions have prompted you to have formed such an opinion, and hopefully I can redeem myself by reference to the document to which you provided a link (with which I am already familiar).
The document covers both the AJ6 and the AJ16, although obviously we are only talking about the AJ16.

Page 29
​​​​​​AJ16 4.0 Liter Engine Management System
Throttle Position Throttle position sensor (TPS) The 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. The ECM applies 5 volts to the sensor and monitors the voltage across the pins to determine throttle position: low voltage – closed throttle, high voltage – opened throttle

Page 39
​​​​​​AJ16 4.0 Liter Engine Management System
The nonadjustable fixed idle air bypass provides a base idle setting. The ECM-driven IACV provides a variable idle air bypass enabling ECM idle air control. The nonadjustable throttle position sensor provides the ECM with a throttle position input. Refer to page 29. The throttle valve will not require setting during service.

Page 40
AJ16 4.0 Liter Engine Management System Idle Control (continued)
ECM Idle Speed Control ECM idle speed control occurs at closed throttle when road speed is less than 3 mph. The programmed idle speed accounts for engine temperature and the loads placed on the engine by the transmission (gear position N, D, etc.), and air conditioning compressor clutch operation. Target stable idle speeds: Park / Neutral – 700 rpm (normal operating temperature) Drive / R, D 2, D 3 – 580 rpm Idle speed ± 30 rpm when coolant temperature is less than 86˚F (30˚C) Idle speed ± 20 rpm when coolant temperature is 86˚F or higher An ECM adaption function allows for a correction to the idle speed “base line” as the engine base idle changes with age. The adaption values are held in nonvolatile memory (EEPROM) and will be retained even if the battery is disconnected.

Page 53
Limp Home Default
In order to allow vehicle operation if a malfunction occurs, “limp home” default values are incorporated as an ECM facility. If a sensor fault is detected by OBD, the ECM will substitute a nominal value for the missing input(s).
(This latter point would explain why most cases of high idle complain of the same Rpm range. The AJ6 manual suggests the default value is 1.5v)

Interestingly, I could find no reference to a procedure to set or adapt the throttle position sensor or idle speed. on the AJ16.

Correct me if I am wrong, but the AJ16 manual would seem to support everything I have hitherto asserted in relation to idle control.

On the other hand, in the AJ6 section of the manual, there is talk of of adjusting the throttle position sensor and a process involving adaption on JDS, but I would not for a moment suggest that you may have used the wrong manual to arrive at the views you have been expounding regarding idle control.

 

I agree, I am only referring to the AJ16 engines. I am not familiar with the AJ6 engines.

As you yourself have highlighted above, replacing a TPS when the ECU has adapted to a new idle position will not cure the problem. Only a TPS reset by a PDU/WDS/etc can perform this reset. Afterall, since the ECU has adapted to a new idle position, it needs to know if you are replacing the TPS with a new one, which can only be done with a reset. (That is precisely what the PDU and WDS ask you to confirm before it resets the TPS) This is why simply replacing a TPS for a high idling engine will not solve the problem.

The manual is correct when stating that the TPS is fabricated as being non-adjustable, however, enlargening the holes modifies it to now be somewhat adjustable. This is usually enough to adjust the new TPS to match the new idle position the ECU has adapted to. If the ECU has adapted to 0.62v being the idle position, installing a new TPS may show a 0.59v when at idle. That's enough to run the engine at a high idle, since the ECU thinks the butterfly is slightly past idle. A new TPS could coincidentally match the previously learned position, but that would be a coincidence.

Cleaning the throttle body can also have the same effect. Over time, with age, the butterfly cannot close to the specified .002", due to gummed up parts, or stretched cables, whatever the cause may be. So the ECU learns that 0.63v is the new base idle position. So now when someone goes in to clean the throttle body, the butterfly can go back to the engineered .002" and the base idle position is restored to 0.60v...except that the ECU is still expecting to see .063v at idle. So guess what happens....that's right, high idle.

 

We had a form we would fill out to correct the Boeing manuals.as manuals are not always correct but we would sign that we followed them to a T on every job admissible in court

To deviate from what is written at that point in time took engineering approval before releasing the aircraft.

I was once belittled by a passenger telling me he could solve an issue faster on a flight delay so I asked him what he did for a living and he said he was a Electrical Engineering professor.

I looked at him and told him I don't have time to teach him real world engineering and the look on his wife's face I will never forget.

I hated differential equations.

 

I have been following this debate with interest, it seems to be an age-old debate when looking back in the forums.
Vee, it was a shame you did not include the manual I have downloaded here which covers the topic with more info.

John Herbert
1996 XJR

 

Further to my previous post, I did mean to refer specially to page 25 to 28 which covers the TPS.

John Herbert
1996 XJR

 

Thanks for attaching. No doubt this will be valuable for people in the future.

I now have both a PDU and a WDS, so I no longer have to worry about TPS resets, however before I came across these tools, it would have cost me $150 and days without a car if I didn't learn how to modify and adjust the TPS.