Just an update for posterity and to put a bow on this thread since it was frustrating for me to search for threads and then read them only to be left hanging because other OPs didn't update with the issue resolution.
Recap: 2017 BRZ 6MT, bone stock never modified, original owner, 27.6k miles, all maintenance performed by the book, driven conservatively, never tracked. P0300 and P0303 misfire codes. I was 1 month past the expiration of my 5 yr powertrain warranty. It was not a spark or fuel issue.
The issue was a fractured valve spring (I didn't bother to ask if it was an intake or exhaust valve) in cylinder 3. Luckily the valve didn't drop and cause any further damage. The dealer removed the engine, opened the heads on both banks and verified the one spring in cylinder 3 was the only fractured one. They replaced all 4 springs and valves in cylinder 3 and reinstalled the engine in the car. Total cost for parts/labor/tax: $5044. For various reasons (dealer tech shortage, queue of other cars at the dealer, parts availability), it took 2.5 months from the time I dropped it off to the time I got it back. I actually had to buy an OEM catalytic converter gasket from eBay myself and give it to the dealer to enable them to reassemble everything because that part was on national backorder and they wouldn't have been able to obtain it through official channels for at least another month
After painstakingly making my case, SOA offered a $4000 credit for the repair so I was out of pocket for the remainder. I received the car back a week ago and it ran fine for the 40 miles I put on it before I sold it to a well-known used car retailer.
Why did I sell? Well, how would anyone be able to trust the other valve springs that were not replaced? This was a bone stock car that was maintained and never abused. It must have been a bad batch of springs.
Why didn't I ask to have the other valve springs replaced? It may be just me, but I can no longer trust an engine after it's been opened and knew I was going to sell the car regardless. I wasn't going to pay more to get the other ones replaced.
Anyways, I love the chassis and handling of these cars but have had the worst luck with the turd of an engine that the FA20 is. I was ok with the fact that it makes no power, no torque, has a torque dip, isn't smooth, doesn't sound good, etc... but to also have it be unreliable is just
The BRZ was actually my second twin. I also had one of the first 2013 FR-Ss to arrive in the states, also kept it bone stock, maintained it well, tracked it 4 times and it broke a valve spring (it was one of the early casualties to the issue that we all now know as the J02 recall) and dropped a valve after 35k miles (covered under powertrain warranty).
I love the 2nd gen GR86/BRZ but just can't get myself to go for one after all this. But hey, maybe 3rd time's the charm?
