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When is a throttle adaptation required, or just prudent?

XJ XJ6 / XJR6 ( X300 ) 1995-1997

When is a throttle adaptation required, or just prudent?

Old 05-01-2019, 07:52 AM
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Question When is a throttle adaptation required, or just prudent?

Over the last couple years, I've taken the throttle body off, cleaned out the LOADS of oil gunk around the butterfly, the return spring on the TB was changed per recall, and now I have a new IACV installed.

If you have a lot of time and patience, you can see part that adventure here:


The car is running and idling fine now, albeit just a tad high which at this point I'm OK with, and pulls away cleanly. As far as I can tell there is no problem with air/fuel.

But I've heard in the past that when one performs any work that could cause the ECU to have it's sense of fully close to open TB butterfly or other significant airflow changed, one should have a "throttle adaptation" performed, which can only be done at the dealer (or someone with WDS).

So, what are the thoughts of when it makes sense to have a "throttle adapation" performed, and also are there any other "adaptations" that should be done concurrently that I would want to make the dealer aware of?
Old 05-01-2019, 08:21 AM
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Plug an OBD scanner, key in position 2 so you can see full live data and check TPS operation range and post it here what the 'fully closed' position is, should be ~13% or 0.6V with foot off the pedal and then floor it and again check the value, should be as close to 100% or 5V as possible. If these values are different then yeah, throttle adaptation and further setup might be a good idea.
In a perfect setup, you need throttle gap when closed set to 0.002" with TPS showing approx ~13% or 0.6V and then as close to 100% or 5V at WOT. Obviously adjusting TPS, affects gap and the other way around so when setting this all up all three have to be taken into an account.
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Old 05-01-2019, 11:31 PM
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In my opinion and I can be wrong the adaption is a factory preference setting to have the car run correct the minute it rolls out with the TPS matched and the O2 sensors tuned

With the advent of the test equipment disappearing ( and cost ) forces looking at it from a different approach and this is where I stick my neck out being this my first Jag this last year

I am assuming the O2 sensors can learn and adjust over time as they change performance . A sudden change of all 4 could be out of reason for the ECU to get it together and have a decent engine regulation performance

On the TPS a trail and error may be the way to get them to match without being able to orient the ECU

With the range of 0.60 + or - 0.02 volts DC on the middle wire of the TPS connector you don't know where the ECU is oriented to so it would be trial and error to put it on 0.59 or 0.62 and see how it runs

It can be done with the TB still installed and the mounting screws under there but takes alot of patents

It can be read and adjusted with the key on / engine not running

With a new TPS the mounting holes have very little if no slack to adjust but drilling up a size gives you wiggle room

Mine was set at 0.63 volts for whatever reason but I suspect a new one was just slapped on there and never saw a Jaguar dealership

This car was lost , but found

PM and Edit now work

Last edited by Parker; 05-01-2019 at 11:54 PM.
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Old 05-02-2019, 07:17 AM
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Thanks for the tip to get some stats katar83, I'll try to do that this weekend.

Regarding twisting the TPS, that's nigh impossible on the supercharged cars while on the car as the TPS is facing the engine block and there is very little room to get tools or hands in there. Possible maybe, but tough.

Although not necessary, I take the car to our local Jaguar dealer once every couple years for a "look over" so maybe I'll just have them do the adaptation then as a "tune up" after all this work. They seem to get a kick out of a 23 year old Jaguar coming in for service that also is still in very good shape
Old 05-02-2019, 04:31 PM
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You shouldn't need to perform a a throttle adaption, unless you change the sensor, move it on the throttle body or adjust the throttle stop to a more open position "at idle" or replace the whole assembly. Even if you change the throttle body you could get lucky and fit one with a lower closed throttle voltage than the one that you removed. In which the ECU will adapt downwards. The ECU can't adapt upwards without a "throttle adaption" being performed using WDS or similar equipment
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