I know there are numerous threads open about such issues, and I've read a number of them. I figured it would be better to start a new thread, though, instead of piggybacking on another. My 2013 Prius Gen 3 with 266k miles on it started doing some intense rattling/shaking at startup about a week and a half ago. It was on startup but also when accelerating from some stops. It started rather suddenly too. It also threw a P0302 code (misfire on cylinder 2). I started with replacing all spark plugs and the coil on cylinder 2. Still knocking. But only on initial starts now. I put the original coil back in, no change. I found posts on the T-SB 0012-10 referring to a defective intake manifold under those exact conditions. So, I replaced the intake manifold, cleaned the engine intakes thoroughly, cleaned the PCV valve, and did a precursory EGR cooler cleaning (it could use more cleaning, I was eager to get it back on to test for head gasket failure). The EGR was pretty clogged up, again, got a good amount out. The old intake had a fair amount of milky liquid at the bottom. But I read this is normal. Still knocking. Much less severe. Only on some startups. No codes but monitoring it at startup shows there are still misfires on cylinder 2 on startup (just not enough for a code?). The coolant level was a little below low when the knocking first started. I don't know if it had been like this though. I've since topped it off and seen no noticeable drop. I also did a block test/combustion leak test. I put the tester on the ICE coolant reservoir, ran the car up to 190 coolant temp, and did the test. Pumped for two minutes. The liquid was still blue. I also peered down each cylinder (plug and coil removed), each looked dirty. I read that if you have "steam cleaned" cylinders it's a sign of head gasket failure since burning coolant cleans the cylinders. I'm on the verge of taking it to a shop for further diagnosis. Going to talk to a family friend mechanic later today but looking for other things to check. Someone mentioned a leak-down test. I'm not sure where to get that equipment. I rented the block tester from O'Reilly, I didn't see any leak down test equipment for rent. I've somewhat come to terms with the idea of it maybe being the head gasket. But I can't confirm it. If it is, probably going to sell the car. I would love to attempt a head gasket replacement but I don't have the time or space (I live in an apartment complex). I'm leaving the country in 4-5 months and my motorcycle will do just fine for me until then.
Update to this while I've been waiting for it to be approved: I took a look at the fuel injectors. Looking at just the electrical plugs, the one for cylinder 2 was damp with what looked like oil. The other three were dry. I removed the injectors for cylinders 1 and 2 and swapped them. All of them had a fair amount of crud built up around the nozzle/shaft, but cylinder 2's was noticeable worse. Gave both a wipe off on the tip before putting them in. I will add that when I started the car again there were some misfires on 1, 2, and 4. I'm wondering if it may have had something to do with the fact that when I removed the first injector for swapping, the fuel rail was emptied.
