S40: S40 T4 98y No idle; EFI-256

[Endorphin]

Hello colleagues.
So the car is S40 t4 98y with a lot of things repaired in 3 months up to now.

When starting the engine for 1st time after finalizing the fuel system, I noticed there is hiss-ing sound from one of the Quick connections to the Fuel rail lines. In a bit of a positioning it better it spilled a bit of petrol and it stopped hiss-ing. The petrol spilled right on the cable branch for the Coil cables and on one of the Engine ventilation hoses i suppose.
To check whether i fixed it, I powered up only the fuel pump with additional cables, and the Car battery wasn't connected then. The Fuel pump cables however were. (external fuel pump)

When fixing the hiss-ing connection, at attempting to start the engine once again it had no Idle.

So not it shows EFI-256, after driving a bit is showed also front and rear O2, but i think i know why.
About EFI-256, i checked the engine relay and it is working fine (although i don't know exactly why it is for).
I replaced the Idle Control Valve (first cleaned mine, it didn't changed the situ) and with the replaced valve, when i Delete the Error code it revs a bit (to 3000rpm) and the light comes on on the dashboard and it drops again.
It actually has an Idle which is arround 500rpm, the vac at this Idle is still -0,7bar (on boost meter). When I remove one of the vaccum hoses, it goes up in rpm to arround normal ones. So it needs more air i guess.

When driving, from time to time without changing the position of the throttle pedal, it runs like i did pressed it, and then again goes to normal. So it engages the Idle Control Valve i guess, because when it happens, the vaccum in the Inlet Manifold also drops, so - it has no other possibility to get the air insite the manifold.

Not too short, but ...
Diagnostics and Error codes readouts made with Delphi.
I have also VolFCR, but I dodn't had the exact computer then.

So it had previous problems with Coils cables.
Can it harm smth when externally powered up the Fuel pump, and can the fuel make some problem on the cables - what to look for?

I found one thread rather actual, but it doesn't have a conclusion
https://www.volvoforums.org.uk/showthread.php?t=287353

Excluding the poor Idle and the error code, the car runs fine.

[Endorphin]

It is EFI-254, not 256. My bad.

[Endorphin]

Somebody to know how this Error code is generated atleast?

[Endorphin]

The problem was - me, to put external power supply to the Fuel pump, causing the ECU to burn a track in the circuit board.
So the attached is how it is fixed (temporary, but for 6months still no issues so far).