Gas Engine Shakes at Startup

My 2012 Prius V recently passed 100K miles.

From the advice on the forum, I did some recommended maintenance.

• Cleaned Intake Manifold
• Cleaned EGR Pipe
• Replaced the PCV Valve
• Replaced Air Filter
• Replaced Fuel Injectors
• Oil Change

The air intake manifold, EGR pipe, and fuel injectors all seemed to be relatively clean. However, about a week after I did all this, it began to shake when switching to the gas engine. It does this most aggressively after the engine has cooled down.

Here is a video of the sound:

The check engine light came on and it gave me P0300 (random cylinder misfire) when I ran the codes. After this I replaced the all the spark plugs and checked the ignition coils with a multimeter (they seemed to be working).

I also remembered that when I filled the oil, I added 5 quarts instead of 4.4 quarts. So, I drained and changed the oil again. When I drained the oil, it was a translucent amber color and did not contain any contaminants.

After running a bit with the new oil, the check engine light has turned off but the engine still shakes on startup.

I used a combustion leak detector as well, and the fluid did not change color at all.

I'm wondering what I need to do from here. What is the next diagnostic I should run and what could be causing this?

 

I checked all the cylinders with a borescope. Cylinders 1,3, and 4 all looked similar. They had a dark residue and looked slightly wet. Cylinder 2 was, however, very dry with little residue. I tried to see if I could find any leaking in the cylinders while the cooling system was under pressure, but the borescope I was using didn't offer a very detailed picture of the sides.

I assume, at this point, there is a leak in the head gasket. Before I go about disassembling the engine to replace the head gasket, are there any more tests I can do to understand the extent of the damage? How would I discern whether I would need to replace the entire engine or just the head gasket?

 

I haven't noticed any leaking in the cooling system yet, the spark plugs were clean when I pulled them, and there's no white smoke on startup. I'm still assuming that it's a head gasket, but hopefully I've caught it early on and the damage hasn't warped the head or bent the connecting rods.

I've probably driven only five miles since I first noticed the issue, since then it's been parked. Luckily, I don't need to drive it until I can fix the issue.

I'm going to attempt to replace the head gasket this weekend. It's not a repair I've done, but I feel relatively confident under the hood and there are some very in depth tutorials on YouTube.

 

I wanted to circle back here with an update.

I finished the head gasket replacement. It was a bear.

Since then, I've put about 500 miles on the car and seems to be doing well.

It hasn't inspired much confidence in my car (or the brand) though. Even with a new head gasket, I haven't solved the underlying problem in the engine that caused it.

I've been looking for the reason that these Gen 3 engines are prone to head gasket failure. It seems like there's a lot of conjecture without a ton of evidence. I know there's a whole lot of collective knowledge in this forum, so maybe I just haven't found the right thread. I'd appreciate it if anyone could point me to some further reading on this.

I'm hoping that this repair will last me at least another year. Hopefully, the used car market will cool down by then and I can buy a reasonably priced Honda that will end up disappointing me as well...