Diagnosing and Repairing a Misfiring Subaru Forester: A Mechanic’s Journey

Well, apparently today is Subaru day. We got this 2,019 Subaru, also a forester. And it is, uh, misfiring at idle. Coming up with a P 0 3 0 2. I did hear a little bit of a weird chattery noise. I wanna listen to that. Alright, no real big difference in noise side to side. And we turn this off before it gets too hot. All right, coils are swapped. I’m gonna clear codes here. I swapped, um, coil No. 1 and coil No. 2. Let’s try roughness monitors. Actually, cylinder 2 still misfiring. And depending 3:02. So I know the misfire detection is on point as per which cylinder it is. Alright, the plug doesn’t look horrible. It’s also not wet. Alright, let’s see if it fires. Well. Up here is a much better view. Look at this. I’m looking in cylinder. Is that rust? That’s rust. Nice pitted valves. Good god. Cooling off for a second. So here’s the thing is, these engines aren’t known for head gasket issues. I’m thinking that that’s carbon deposits. That looks like rust. Um, I’m gonna see. I’m gonna throw the battery in there real quick, crank this thing over. Compression should spit fuel out. So it’s direct injection. I, I should have fuel spitting out at me. This is way easier to do with another person. But look at that. There is so much carbon on these valves. See if I can get this out for you. I mean this Is this has got to be the source. So much freaking carbon. And the valve face looks like crap. The seats actually look kind of look better here than the exhaust side. I mean, maybe not, but um, the freaking valves themselves. Let’s do that same trick and see if it works. Yeah, these just the valves. Alright. I really think this might be a carbon issue. Or a carbon issue. That went too far. What I’m gonna do to verify that is gonna be an old school trick. But I gotta get all this set back up. All right, old school trick. Car is down to base idle and go over for a very simple vacuum gauge between. I don’t know if we could pick this up on camera, but we got a bouncy needle between 17 and 18 inches of mercury. Unfortunately, by the time I got back over to that thing, this engine had warmed up a little bit. And um, the. The misfire is uh, is gone now. Um, before it warmed up enough, it was in a high idle. That needle was much bouncier. It’s gonna be carbon on the valves. Um, you guys let me know you what do you think of those valve seats and the valve faces themselves. You think they’re gonna be recoverable? And as you can see, as we’re warming up, our needle got steadier. Our vacuum is becoming closer to 21. After seeing that, I feel pretty good about The valves. Um. I’m gonna say that’s a diag