Breezy_Pete

The description of the windscreen for the provided VIN, of a car with heated windscreen is: "Heat insulating windshield". To me, that didn't sound like a convincing description of a heated windscreen, so I suggested that you might be able to confirm. PR code was 4GW. I have (paid) access to partslink24, but not always much knowledge about what I'm looking at.

Maybe measure the 5V supply that goes to both the EGR valve potentiometer and the MAP/IAT sensor. Red/green wire at each of those connectors, measure relative to the brown wire at MAP sensor, and relative to the brown/blue wire at EGR connector. Ignition/contact on, or engine running when measuring.

In a LHD car (steering wheel on the left) it is somewhere just above your left foot when driving. Onboard control unit is often called 'BCM'.

Does disconnecting the EGR plug generate fault code(s) and fault light? (asking @Erdmi )

Surely that would generate a fault code?

Yes, it causes owners in RHD countries plenty of head-scratching. Cost saving.

OK, I give up. ☹️

No, you just have a RHD car instead of the LHD the manual pictures. Fuesbox is just rotated 180°, in the factory.

Another possibility, I guess, is that the catalytic converter is blocked to some extent, causing the exhaust pressure entering the EGR valve to be higher than mapped. The feedback system for EGR opening is based only on physical distance, via a potentiometer in the top part of the valve. So more gas could be flowing through EGR into inlet manifold than expected, causing higher intake temps and poor combustion. How many kilometres has the car driven?

Does the engine ECU log any fault codes for EGR or anything else?

Labelled B above.

It's in the front half of the airbox, the section that does not need to be removed to change the filter. Wedging the flap in the cold air only position is probably the easiest solution, which can be done with a screw. Do the experiment first (running without airbox), I might be completely wrong about why the engine is having trouble.

Are you aware of the warm/cold air mixer system within the airbox? When the wax thermostat in there fails, it leaves the mixer flap in the 'maximum warm air' position. The combination of that unnecessarily warm air and hot EGR flow may be causing the problem.

Can you try running without engine cover/airbox for a short drive when engine is fully warm? See if fault still happens.

EGR flow isn't enabled until coolant temperature is above a certain point, maybe 50°C, Can't remember exactly, so that may be why it's OK when cooler.

Have you inspected the brake servo vacuum hose for cracks and leaks?

Or the bearing didn't go quite fully in on that side. @joeninho is the problem on the first side you did?

^ Wildly optimistic.

I'll send you a message requesting the VIN. With that I will be able to help.

Isn't the thing you are calling 'relay pack' the same thing as "fan regulator - J126'? It doesn't contain any relays, I don't think, transistors instead. Follow Binx1310's link to look. If power is getting to that but not to the fan motor then either that new J126 is faulty, or it isn't getting the necessary information to know what it should do. There is a thin communication wire that tells J126 what to do, coming from the Climatronic module, as @Cairus described a few posts back. That wire may be damaged or have a poor connection at either end of itself.

Might also result in DPF problems if engine management isn't fooled.

Should fail MOT without, but might require quite a thorough tester to spot it. You can get an emulator which plugs into a couple of places and keeps engine management quiet. All a bit illegal, of course.

Damn, google is good sometimes https://www.briskoda.net/forums/topic/497627-oil-sensor-fault-octavia-vrs-2019/

There was a member posting about spurious oil level warnings on a new car of about the same vintage, a few years ago, I think. Dealer had several goes at fixing it. Wish I could remember the member's name. Don't worry about the cold level, just remember how it relates to operating temperature level, for convenience. Some people swear the level will be higher when cold. My experience is the opposite.