TL:DR version: Flashing CEL @ high RPM + consistent misfire (lumpy idle). No codes. Question: Is it a coil, fuel system component, or a dying engine? What to check first?

I could use a second car and a buddy happens to have a 2005 S40 T5 AWD 6-speed(!) that he basically just wants to give away. He's owned it since new, always dealer serviced, so it's had a lot of good maintenance done to it but...it's still led a pretty hard life I think. At least the last year hasn't been good to it; it's been sitting for most of that time.

I drove it the other day and was pleasantly surprised at how well it drove until it got warmed up and I took a couple pulls to high RPM. That's when the CEL would flash and it developed a miss. Seemed to get worse the longer the drive went on. CEL did not remain on. Car started normally afterwards but had a consistent miss regardless of RPM while sitting in the driveway.

No OBD codes present. The last time it was serviced there was a misfire code for cyl 3. Which was diagnosed as a faulty coil. It and the spark plugs were replaced.

Lacking codes I'm concerned that it's not just another coil or a faulty injector but could be a dying cylinder. I'm willing to take a chance but I don't have much time and money to throw at this thing right now. What should I check on this warlock before I go to the trouble of buying it?

Thanks a bunch.