3/4 then 1/2 misfire codes? (EJ25)

[Red92]

Hey everyone. Have an interesting puzzle here.

 

EJ25 in a '99 Outback. Its been running great, but a week or so ago the check engine light came on, and the codes said P0303 and P0304 (cylinder 3 and 4 misfire). My wife said the car lugged a bit at low RPMs right when it happened, but it was running fine after that as well as when I was checking it later that day.

 

Since the two codes came at the same time, I thought it might be the coil at fault. I didn't know how old the plugs were, so I figured it was time for a tuneup and gave it a new coil, new wires, and four new NGK plugs. (The old plugs looked fine.)

 

It ran well after that, just as well as before. But a day later the CEL came on again, this time for misfire codes for the OTHER pair of cylinders- P0301 and P0302 for cylinders 1 and 2. I was along when it happened, and the engine continued running seemingly normally. We monitored it for a few days, and it still idles smoothly, revs, and accelerates under load completely normally. The only observable abnormal thing it did is kick up to a fast idle a few times while we were stopped in traffic waiting for a train to pass. (AC/defrost was not on.)

 

I've done some searching, and found quite a number of things that could cause misfires... But the fact that my misfires were always in pairs, and that the pair moved to the other two cylinders after the coil/wire/plug change, has me stumped.

 

Any thoughts on what I might check next?

 

Thanks

[GeneralDisorder]

Those pair's share one side of the wasted spark coil and one side of the ignitor. Otherwise they have nothing in common. So your potential problems are:

 

Coil

Ignitor

ECU

Wiring

 

GD