[2valves]

From the dates you quote on the parts these would come from the D4192T2 engine? The one with the Bosch rotary pump is what I'm meaning if the code is wrong. These are very thin on the ground now as they were only sold for about 18 months if memory serves. My S70 TDI uses the 5cyl version of the same injection pump and it has a 3 plug version of the same mounted to the passenger side of the engine. I'm not sure if they switch on with the engine glow plugs or are controlled separately, but so far as I can tell there is no way to control them manually to warm the engine before starting (if that's your intention) I think they are to get the engine warmed up faster after it has started. You might get a better answer on how they work if you ask on a Skoda or VW forum as cars with the VP37 pump are still quite numerous especially Skoda Octavia.

I once went down a rabbit hole looking into these plugs myself on my car as it was taking forever to heat up. New engine thermostat sorted that after much wasted time and effort, if that happens to be the issue that has started you thinking.