Hi all, My engine has been having issues for a few hundred miles now. The car is a 2012 Prius with 150k miles. It started during a road trip where the engine would rattle at initial startup and after sitting at a red light for around 10+ seconds. I was getting the P0301 code, and after doing research on the issue these are the fixes I did: - Cleaned intake manifold and throttle body. - Replaced MAF sensor - Replaced EGR sensor and filter - Cleaned EGR pipe - Coolant flush - Replaced PCV valve - Replaced fuel injectors - Replaced spark plugs and ignition coils - Also did an ATF flush twice for good measure Now, while I'm not getting the rough shaking at initial startup or sitting at a light anymore, the engine is still misfiring and every 100 miles or so I'll get a P0300 - multiple misfire code. At this point I'm thinking the only thing left that it could be would be the head gasket, but my coolant level has stayed steady for a few hundred miles so there's no leak there. Could the head gasket be blown without there being a coolant leak? The only other thing I can think of is that the fuel injectors I purchased were poor aftermarket ones rather than OEM and that's what's still causing the misfire. Especially since it went from the P0301 - misfire in the first cylinder to now P0300 - misfire in all four.
The first thing I would have done would have been to remove the plugs after the engine is warm and look and smell and taste or whatever you do at least one two and possibly three and see which one has coolant on it and then you know you wouldn't proceed with the rest of the repairs because you're not going to fix that with any of those but since you've already done all this do you want to pull the plugs that's going to tell you pretty much what's happening It did on mine. And I wouldn't be fixing that engine I'd be looking at JDM replacement or something even though I was 100,000 miles higher than you I would consider that skating on thin ice doing all that work in a z engine but some have.
Here’s what I would do for the meantime. Put a can of BG44k fuel treatment, do a liqui-moly engine flush. Then top off the oil with liqui-moly ceratec additive. Reduces metal to metal friction and smoothes, quiets down engines. I am confident there’s a good chance doing these will fix your issue. My question though, what brand of spark plugs and ignition coils did you use? Because cheap knock-offs can produce your problem. I would use OEM coils and NGK iridiums.
All your remedies to date should have been done at least by 100k. With your symptoms checking and dealing with head gasket comes first.
