Hi,

I’ll start with the first question about a radio suppression relay.
I do not know much about them other than what I have read and the headaches they can create.
I can only imagine that it has something to do with suppressing radio frequency interference from the high voltage side of an ignition system.

I think it all came about on the early 700 series with their Regina ignition system as the 700 ran concurrently with the last years of the 240. The 240s did not get them to my knowledge.
The 700s and the newer FWD 850, that Volvo reluctantly had to build to stay alive, caused more turmoil.
The 700 was too GM looking and wasn’t selling well and the 200 series was aged.
The automotive world was running towards FWD. It’s same with the AWD sales.

In 1989 240 the EZK ignition with the CPS came into operation doing away with the Hall effect triggering sensor in the adjustable distributor for timing. Before LH 2.4 that was driven by emissions tightening and programming that adapts to drivers.
The limited editions of LH 3.1 later in 240s was part that evolutionary process that went gang busters.

Now the EGR controlling valve is a lot simpler and it does make a difference which way the nylon lines connect onto the valve as one line vents the diaphragm since it the port on top.
Nylon resists collapsing.
As I remember I found a faint ink-like dot of yellow near that port because I had the valve in hand. It might have been a residual material from a sticker.
You said know how that goes! You must have a nice looking engine bay to order a decal.

I felt it could be easily overlooked at the time too. I think there is a faintly casted Z too
but maybe it’s a code for vacuum? Maybe Add some German accent and it says 😬 Z vacuum…. 🤭?
So I checked it out by testing and thinking how it operated to fill the EGR line with air to close the valve back shut. Cannot keep the vacuum and just wait as the temperature sensor tells the ECU it changes

As I remember, from 2005 👀 it just popped off, I think I used a knife blade to snap it. It did look fragile but looked molded separately from the body too.
Injection molding has some tells, if you study their methods of “how did they do that?”

But by servicing it once since then, I have kept the light off for about another 100k.
I’m thinking your mileage says it’s due or lines are backwards.
Switching will not do anything if the valve is clogged so test it.
I think I used a nine volt battery as it’s my MO on IAC valves.

Yes, my bed time has passed but a nap with a “Q” says you were tired at some time too. 🥴

Phil