Good morning Bidand,
Great, I'm reensured that the fuel pressure is having nominal values.
As per your recommendations, I did a run and record the engine metrics under load.
Here are the results :
Status : CL
Calculated LOAD value : 57.3%
Engine coolant temp : 95°C
Short Term Fuel trim B1: -1.6%
Long Term Fuel Trim B1: 5.5%
Short Term Fuel trim B2: 3.9%
Long Term Fuel Trim B2: 8.6%
Fuel Rail Pressure : 270 KPa
Engine RPM : 2158
Vehicule speed: 74 Km/h
Ignition Timing Advance: 36°
Intake Air Temp : 20°C --- Comply with the home external thermometer
Air Flow Rate From Mass Air Flow Sensor : 17.08 g/s
Absolute Throttle position: 17.6%. (14.3% at idle)
Short term fuel trim B1.S1: -3.1%
Short term fuel trim B1.S2: 99.2%
Short term fuel trim B2.S1: -3.1%
Short term fuel trim B2.S2: 99.2%

It looks that the values are not that bad
Marc

 

Good Morning DeepSound 80,

Up early I see.

Indeed, not that bad, for both banks running a little lean, more so Bank 2 now.

Now for example, if we were to Drop the engine load and see what the trims do. Like putting your foot on the clutch to change gear, in live data? The load comes off,(your foot off the accelerator & the clutch disengages the engine from the gearbox /drive with other foot pressing down)

Too much fuel for the metered air, the revs increase using the unmetered air, and the O2 sensors require less air/less fuel. Which you see it trying to do with a delay.

All this to explain, you have an air leak giving additional unmetered air to the engine and over run when taking load off the engine.

Granted, It is not enough to throw codes, yet. But give it time.

Again, would still suggest you have an air leak(s), small just now and that is what is causing the issue with the revs increasing during changing gear. Poor performance, and increase fuel consumption, by running slightly lean and the O2 sensors demanding more fuel.

Indeed I find them rather nippy cars, Pre face lift 3.0ltr 2000, (Auto) and equally as good as the Volvo XC 70 (2.4 turbocharged) and a little lighter. So yes something is not right.

Looking at every other reasonable angle, throttle body operation, incorrect air temperature feed back to ECM, we are left with!.......................

A few more posts, and if you google a variety of combinations of "revs increasing while changing gear" (for Jaguar S type V6 2000) you will get a range answers, mostly pointing too slight air leak, or more severe air leaks with codes, P0171,P0174 some solved, and some dying out unanswered?

e.g examples below.

https://www.jaguarforums.com/forum/s...l-down-207931/

https://www.jaguarforums.com/forum/s...ics-faq-52720/

JagRepair.com - Jaguar Repair Information Resource

https://www.jaguarforum.com/threads/...75#post-843775

https://www.jaguarforum.com/threads/...41#post-772041

https://www.jaguarforum.com/threads/...75#post-995575

Todays thoughtful suggestion!

If you have a look at the various photos of the Jag Repair air leak repair. To make sure you have the air/vacuum lines in the correct position/ orientation for less stress on pipes, and fitting, and everything is snug and fitted / routed correctly into place.

Old Adage!
(If in doubt, and nothing is working, go back to the beginning, and start again, because you have missing something.)

By the way, when I had my air manifold, and both rocker covers, and the fuel rail manifold off, I checked all the silicon seals, all were found in very good condition and refitted the same 24 year old seals and joints. Apart from the MIT O rings which I had the new yellow ones. The rubber hoses on the air side were mostly good with little wear, apart from the crankcase breather reducer.

The only air side things I changed were all the crankcase breather pipes. The lower elbow while rather thin, was still OK, the reducer 15mm to 10 mm, was cracking at section change, and all pipes replaces on the breather line were changed to re-enforced silicon hose, ( as what I had in stock) and a brass reducer to make the hose section change 15mm/10mm. All push fit and running fine. On a 24 year old 58K mile car.

But where your air leaks could be! Is unknown, and requires to be fully checked, line by line and fitting by fitting, seal by seal, until found.

 

One thought, under the category of rechecking everything when nothing makes sense:

Make sure the actual fuel pressure agrees with the sensor value. If the sensor is inaccurate, the computer will happily adjust pump output to this erroneous input and never set a code.

On the early V6, there’s a test port on the injector rail. It’s near the oil filler cap and looks like a tire valve stem. Connect a mechanical gauge and make sure it agrees with the value seen by your scanner.

 

Did you skim the plastic lower inlet manifold when replacing the gaskets? They have a tendency to warp.

 

Thank you very much for the suggestion,
I will proceed as per your recommendation, unfortunately not yet as summer vacations are almost here.
I will keep you updated as soon as I will be back to business.
Enjoy your holidays
Marc