07 Type-S (manual), 138K miles, always 93 octane, oil (always synthetic) just changed, no CEL ATM.

From some googling, I'm ~90% sure I've got either a clogged EGR valve or a ignition coil that is going. Car idles a bit rough (noticeable, but not the worst I've felt), but the real symptom is at high gear/low RPM with ~>30-50% throttle I get pretty strong stuttering/knocking. Car does it out of the driveway and after having been driven. Hot or cold day, doesn't matter. I had the CEL flash once when I had a knock, but nothing since then. I'm driving the car as minimally and as softly as possible ATM. So, questions...

1. Does this sound like a bad EGR valve or ignition coil to you?
2. If I had my mechanic ("I know a guy", not a shop) run an ODB scan, would he be able to determine what the issue is, even if there is no CEL (when he does the scan)? I ask because he's been a bit... let's just say, finicky, of late (but very reliable overall) and I don't want to piss him off with a "obvious" question.
3. If the answer to 2 is "unlikely" or "no", then how should I proceed? Is having him open things up the next step?
4. If the answer to 1 is no, what could this be? Then that applied to question 2.

 

Maybe? Hard to say.

A scan will only tell you an existing or pending code. He will need to look at the live data. You will need to look at EGR PIDs, fuel trims,

You should have scanned it when you got the CEL to see what code it gave you.

 

Thanks for the reply. Unfortunately the CEL only came on momentarily (literally a couple of seconds) and then went away (and hasn't reappeared since).

1. Should I ask him to scan the car now?
2. If that the CEL comes on again, but goes away, would the code stay in the system (scan asap)?
3. Should I just wait until the CEL comes on and stays on again? Assuming I drive the car carefully, how much "risk" am I exposing myself to (by driving it)?
4. Should I bother the mechanic? If yes, what should I say/ask?

Things are obviously tight with the current state of the world, so I'd like to avoid this spiraling into a costly situation.

 

1. That's your call. You can also just go get it scanned at Autozone or buy your own OBD-II bluetooth dongle and pair it with the Torque app if you only want codes.
2. Most likely, there will be a pending code or historical code. You might also have a freeze frame.
3. It's really your call on waiting or not. It's hard to say how bad is it right now. Urgency will depend on what kind of code sets the CEL. A blinking CEL is urgent because it's a catalyst damaging misfire.
4. Your call on the mechanic. Just tell him your problem and ask him to look it over. Pretty basic.