2011 Engine rumble when accelerating from complete stop. Just replaced spark plugs/ignition coils

This car is sending me through it! Some history, 'cause I want to be thorough:

Decided to take a long route back from a road trip to California earlier this year. After miles and miles of rough roads through Texas oil fields it started presenting an issue where it would vibrate on start/at idle when the gas engine kicked on. It was very intermittent, but eventually threw a check engine light. I put some seafoam in the gas tank and the rumbling went away, as did the check engine light.

A few weeks later it returned with a vengeance. I tried the conditioner again and it didn't seem to help. We were in the middle of quarantine at that point so not only were there no shops open, I couldn't have friends or family come help me out with diagnosing/repairing the issue. Fortunately it meant that I didn't have to drive much, but you can't avoid it completely. So I certainly made things worse by driving the car while it was having this problem. After a while it would occasionally make a smelly white smoke on startup, and in those instances the Check Hybrid Engine warning would come up. It would also use up coolant. Shortly after this I was able to borrow an old car from my parents and parked the Prius in my garage.

Last weekend I was finally able to get with my folks to work on it. I haven't driven it for a few months at this point. I pulled the codes with a scanner I bought from walmart and got P0300, P0301, P0302. We replaced all the spark plugs and the ignition coils on 1 and 2. We also cleaned out the intake manifold and EGR pipe, and drained/refilled the coolant.

Check engine light is no longer on. I was able to clear the stored DTC codes but they still show up as "Permanent" codes when I connect to the code reader. I'm not really familiar with using DTCs so I don't know if that means the misfire is still present.

It makes the vibration/rattling noise for maybe 2 seconds on its "morning start" now. The car is no longer running rough at idle, BUT will shudder when accelerating from a complete stop (like at stoplights.)

I'm wondering how to proceed from here. I'm thinking I might try to put more conditioner in the engine and see if that helps. My next avenue of investigation was going to be the head gasket, but should I replace the other two ignition coils first? Anything I might not have thought of?

Extra Credit:
Unrelated to the above, but I've also got ABS, Traction, and Brake lights on, and getting that brake actuator noise every few seconds. Brakes still work but are "softer"/less responsive. Lights will go off intermittently and brakes firm back up. I'm aware this was a known issue and recall in the 2010, but not the 2011. However I have seen some stuff about a Warranty Enhancement for this issue that covers the 2011 for certain error codes. I did the paper clip thing to get the error codes and it seems like one of the codes, 69/C1391, should be covered under this warranty enhancement. I have tried calling my local dealership today but haven't been able to get in touch with anyone -- just wondering if anyone here has had any success getting this repair covered by this warranty enhancement (ZJB).

Sorry for the wall of text! I have been lurking on these forums since before I bought the car and this community has been super helpful to me the whole time I've owned it!

 

187k miles, sorry I forgot to add that to my OP!

Risked a grocery store run in it yesterday and the rattle came back once while I had the car parked/running. So she's back in the garage. No coolant loss as far as I can tell but I've only driven it for a few short trips since draining/refilling the coolant.

We did not clean the EGR valve/cooler. I had planned to, basically my intention was to go through all of the NutzaboutBoltz maintenance process, but once we got the spark plugs out they were in such rough shape that I guess I was just hoping that would solve my problems. I actually started to take off the valve cover but the screws were in there tight and I was afraid of stripping them, so I just focused on what I knew I'd be able to accomplish in the day.

We cleaned the intake manifold very thoroughly but I'm not sure about the EGR passages on the manifold. I saw someone mention it in the comments on the NaB video but I'll admit I couldn't quite figure out what they were referring to. I just scrubbed the thing as best as I could following the video, left it in the sun to dry for a while, wiped it out and put it back on.

The EGR pipe was pretty packed with buildup. I knew I should have cleaned the cooler/valve too but I didn't realize until doing more research after the repair attempt that it was probably the most likely point where this all started. Maybe if I'd realized that when I first started having trouble it wouldn't have gotten this bad, but hindsight is 20/20 lol.

Thank you @Mendel Leisk for the tips on doing the cleaning! I'm gonna try that again and make sure to get the EGR cooler as well. See if that makes any difference at all. I'll give a shot at switching those ignition coils too for shiggles.

If the head gasket has failed, which I'm pretty sure it has, I think my next step will be trying to get a low-miles engine replacement. I see there are some resources on the forum about that. I haven't been able to find much about doing just the head gasket, I saw one video series on YouTube that had loud music and no voiceover and just watching it stressed me the hell out. I'm fairly comfortable DIYing stuff and I'm lucky that my mom is a pretty skilled mechanic, but we're not sure about doing that job. At this point it seems like putting in a low-mile engine might be a better investment than just doing the head gasket, even if we have to pay someone to install it.

Sorry for my rambling, I'm just kinda thinking through this situation and hoping I'm on the right track with it. I like this car a lot, I want to keep it for a while!

 

Back with some updates!

Tried swapping ignition coils as suggested. Test drove with no issues. However got a new code when we did this, P0010. Tried test driving again later and the shake was back.

Decided to focus on cleaning the manifold/egr. Got that done. MAN that EGR cooler is hard to take off!! Soaked the cooler in Purple Power then blasted it clean at the car wash, can now see through it end to end.

After reassembling Engine Misfire codes are no longer present. Some shake on initial startup, none whatsoever during test drive. Idled for a while in garage with no issues.

Still showing code P0010, after test drive also shows code P0012.

Death rattle was back this morning on cold start. Seems a little different, more of a clatter/rattle than the previous rumble/shudder. Don't know if it matters.

After doing some research, I changed the oil/filter to see if it would allow me to clear the new codes. No luck. I also tried replacing the VVT solenoid. No luck.

So now I've got new ignition coils and spark plugs, a sparkly clean intake manifold and EGR cooler, fresh oil and a new filter, and a brand new VVT solenoid. I still have codes P0010 and P0012, a loud clattering rattle on startup, though it doesn't seem to be doing it at idle or when i accelerate from stop anymore. No smoke or coolant loss that I'm aware of, though my test drives have been very short.

I was hoping that I'd get lucky and the culprit wouldn't be the head gasket. Could something indicated by these trouble codes cause these symptoms to reappear? I'm going to be doing more research tonight but if anyone could point me in the right direction I'd appreciate it!

 

Aaah! Possible culprit for the P0010/P0012 codes!



This wire was NOT broken before, but it's snapped off from my toolin' around in there. Maybe it was already loose and causing the code. Since it first appeared after swapping those ignition coils it's possible we knocked that connector around too much while changing coil 1. I guess my next step is to get a new plug and see if that'll do me.

Fff all this tinkering I'm doing on this thing I might just have to figure out doing this head gasket myself lol

 

Aight, spliced some fresh wires onto that plug we broke and that took care of the P0010/P0012 codes. Really should have checked the voltages on that BEFORE i bought a new solenoid

I've got NO check engine light and NO codes as of tonight, but still getting some engine shake. Not nearly as bad as before, and it kinda seems like it happened less and less over the course of my test drive. Maybe there's still degreaser in the intake from cleaning it. Maybe there's a tool lost in there somewhere. Idk but my journey's not over yet apparently.

@Mendel Leisk thanks for the link to the video! The only one I'd found that came close was the one from Ebn C on youtube. It seems pretty thorough but there's no voiceover or explanation, just a recording of the process with loud music played over it. I had managed to hunt up some pages from the repair manual to compare to what he was doing, but if you have some excerpts you could send me I'd appreciate it! If we decide to tackle this job I will probably just pay for access to the toyota manual and print out the pages I need, but it'd be good to study up in the meanwhile.

 

Just wanted to post an update! It took us 2 weekends and a lot of cussin' but we got that head gasket replaced at last! Had to chase down a couple more codes for wiring that got damaged during the repair (nothin' a lil' soldering couldnt take care of thankfully) and the thermostat housing leaked a ton of coolant at first (probably just the gasket failing to seal but we put a whole new part on there because good lord that piece is hard to take off without taking the intake manifold back out) but WE DID IT!!

No rumble, no codes! Saved a ton of cash and heartache! And to think I was seriously considering pouring thermagasket down the poor thing's gullet lol

Thanks so much for y'all's advice and support, especially @Mendel Leisk for coming through with all those resources and repair manual info. Also just wanted to update for @Jamendan and @Brian farrell that the head gasket ended up being my issue. It's a beast of a repair, but if you've got the tools and a helping hand or three you'll probably get out of there for <$500 if you want to DIY it. Bonus that you'll learn a LOT about the mechanical parts of your car. I feel pretty confident changing oil and fluids and small parts like thermostat, water pump, etc now when I had no idea how to do any of that before. And if you completely beef it, you'll probs spend less swapping out the engine at a neighborhood mechanic than you would swapping the gasket at a dealership, and that alone made it worth it for me.

Best of luck to y'all in getting your issues resolved, and thanks again so much to everyone who's helped me out