AP0507 can be any or several of these things:
Vacuum leak
Leaking EGR valve
Leaking air intake (after the throttle body)
Malfunctioning positive crankcase ventilation (PCV) valve
Dirty/damaged throttle body
Bad idle air controller (IAC) or circuit
Faulty connection or wire

The P1229 diagnostic trouble code indicates a sensor
power supply circuit shorted. This means that there is
a problem with the power supply to a sensor in the vehicle,
causing a short circuit. This can affect the vehicle's
performance by causing issues with sensor readings,
which in turn can impact fuel efficiency, emissions, and
overall engine performance.

The Diagnostic Trouble Code (DTC) 1612 for a Jaguar XJ8
typically indicates an issue related to the Immobilizer system.
This code suggests that there might be a problem with the
communication between the immobilizer and the Engine Control
Module (ECM).

Here are some possible causes:

• Faulty immobilizer control module.
• Issues with the wiring or connectors between the immobilizer and ECM.
• Problems with the key transponder.

Please note that faulty wiring/connections appears often in these codes.

I am not quite sure how my post ended up in the XJ40 section However Don
helped me to find it....Thanks!

 

Hi Randy,

I think you posted your answer in the wrong thread.

 

Well sir...on 5/24/2024 you posted these codes as pertaining to your troubles.
I responded to them with the thought your issue may be more one of wiring
or electrical fault than a general particular component.

 

Oh yes! Sorry, my mistake. I had completely forgotten about those error codes, they never came
back luckily.

I came across another post where someone had the same problems as me with hardly any sensor
values ​​from a specific bank of the engine. He advised to bend the pins of the plug up a bit so that
they always make contact.
Now have O2 values ​​on both sides again and normal LTFTs and STFTs .

Unfortunately, the problem of the strange "hard" idling and hardly having to give gas while driving is
not over yet. I really suspect leaking injectors or a leaking fuel pressure regulator to the vacuum
hose. However, this regulator is made of unobtanium (part number: C37021 or 96JV-9C968-EA).

I will try to temporarily disconnect the vacuum hose to the pressure regulator, see if that has any effect.

 

Clean the throttle bore, plate; check the air filter; clean the MAFagain. Run a can of a good fuel system cleaner through a tank of gas (I like Gamout's SeaFoam look-a-like; or SeaFoam).

 

Hi Jim,

Thank you. Today I cleaned the throttle plate, bore and MAF sensor as you suggested. Airfilter is almost
new so no issue there. Added a fuel system cleaner from Wynn's.

Just out of curiosity I also checked the fuel pressure regulator with a vacuum hand pump and saw that it
could not hold a vacuum.. It instantly starts to drop, very fast. The vacuum hose is a couple of months
old (replaced all of them a while back, because one of them had a crack in them) and didn't have a strong
smell though.

My vacuum hand pump is working properly, because I also tried to connect the vacuum pump to a
sealed piece of hose to see if this could hold a vacuum. Fortunately, it did.