P0300, Rough Idle Out of the Blue - Anything other than spark plugs before road trip?
 

I was getting ready to go back home with my 850 mile drive and started up the car this morning. I noticed heavy fuel smell immediately. After driving a few miles, it felt like the car had more vibration, even during idle. Idle RPM initially seemed fine at around 700 RPM, but I could feel more vibration and hear the "subaru exhaust" noise. I remember this happening when one of my coil packs went on my old Acura.

After a couple of more miles, the Service Engine Soon light started blinking. I checked the code at Autozone and got the P0300 random misfire. Now the idle is at 1000 RPM and the noise/vibration is worse. I bought 6 new spark plugs from the dealer and am about to do that and clean the throttle body a bit while I'm at it.

I got 95k miles, catback exhaust (stock cats), K&N air filter, and it has been running fine until this morning. I changed out the leaky fuel dampener maybe 10k miles ago. My exhaust might be leaking a little, but this issue came out of nowhere and have had the exhaust/air filter on for 20k+ miles, so I feel like that isn't the issue. It was kind of cold this morning (40ish), but it was in the 30s the week before and didn't have any of these issues. I thought maybe I got bad fuel, so I topped off from another gas station with about 5 more gallons.

Anything else I should try?

I'd try cleaning the MAFs. It's a cheap and easy job, so, even if it is not the problem, you're not out a lot of time and money.

You might want to look into cleaning the TBs, also. And the injectors.

Thanks. I replaced all the plugs, cleaned TB, and the MAFs...same issue. I unplugged one of the front coil packs, and noticed the sound engine didn't run worse when that one was unplugged. I replaced it, and it seems to be running fine now. I got lucky that one of the front coils was bad and I could unplug it while the engine was running to figure out which one was bad.