Rough idle, shaking and FF34/FF36

XJ-S
1

Xjs 1992 v12, 5.3, marelli
I have been trying to figure out this problem for a while now.
So, car at idle does run rough, it’s not missfiring, but I do feel uneven shaking and it’s getting worse when car is hot(after a drive) it’s more or less the same in all gears.
I don’t feel anything when on the road, I wouldn’t bother, but I’m chaising also a very strange overheating as well and thought that it might be connected

Ff34 and ff36 randomly pops out usually after 5 mins of idling, sometimes gone for days.

What’s been done
Both new 02 sensors
Both new camshaft speed sensors
Injector and ignition loom redone
Injectors cleaned and tested
New spark plugs
Both new coils and ign amps
New dist cap
Tried with another ECU
Vacuum checked , no leaks
New fpr and fuel pump
Every injector is clicking, tried to disconnect one injector at a time - nothing
TPS - correct
Blades adjusted 3 times

The only thing I know is that when it hot it’s getting worse and it overheats more when it’s already hot(don’t ask me, it’s a 2 years story) forget about overheating, anyway v12 shouldn’t feel like a 2 litre old diesel track, it’s really massaging my a** on idle.

P.s Cats not clogged

Also, I have been dealing with defected new parts a lot, so don’t cross out some new parts that I have put.

2

Ok I just checked everything again
Just to add
You can feel bumpy idle more on Drive, then park, but I think that’s due to lower rpm on drive, so it’s more noticeable, I checked again with another coils, another amps, another ecu, checked marelli ecu and main ecu vacuum lines, checked cts, ats.

I don’t know , this bumps are really random, can’t figure out which bank is doing that.

While I was checking everything and car got worm , it’s became twice more noticeable. So it’s definitely temperature related

3

Hello Timur - have you checked the motor mounts condition - just wondering if they are worn out - Tex.