Engine knocking/shaking upon starting, but not every time ??

Check the coolant level for the engine the big tank on the left.
You might have misfire codes and have high mileage.

Lots of tinkering around to do if you can DIY.
Time time to clean the EGR and Intake Manifold.

Get those codes read so buy a Carista and download the Dr. Prius App.

 

do you ever shut the car down with a cold engine?

 

Definitely get the codes read. At 210K miles, the EGR components, and the the EGR passages in the intake, will likely be near-totally clogged with carbon. In particular the intake passages, with complete clogging commencing at cylinder one.

Codes:

p0401: indicates insufficient EGR flow
p0300: indicates misfire
p030X: indicates misfire at specific cylinder (X sub'd by 1 thru 4)

If the code is p03... I'd go to a leak-down test, to determine head gasket condition. Boroscope inspection of combustion chambers (for evidence of coolant leakage) is good idea too.

And probably never had EGR/intake cleaned. Debatably at least 110K overdue.

 

Similar problem here (2014 Prius 2, 195k miles).

I had an issue a few days ago, which I thought was my tires losing traction on wet pavement. (Tread was low, and it had been raining quite a bit.) When I would accelerate, there was a stuttering, which felt like something slipping. I knew my tread was low, so I went and got a couple new tires put on. (No regrets about that.) As I left the tire shop, there was a kind of rattling sound near the FL wheel as I accelerated, and the ICE kicked in. The check engine light came on. The stuttering I had experienced before happened again on SOME acceleration..

Took the car to my mechanic after scanning it and getting p0301. Soon as I said what it was doing, they said it needed a new coil, and they did all 4 spark plugs for good measure. (No telling when they had been changed last. It was before I bought it used.) It seemed to mostly correct the problem. Fast forward to this morning. First start of the ICE gave shuddering and shaking. Back to the mechanic, who cleared the engine light again. I mentioned it only seemed to happen on starting (far as I could tell at that point), and he said I should drive for a few days to see if the problem gets worse.

Today, I watched for patterns. Any time the car sits for a short time (long red lights, picking up passengers, etc), acceleration results in shuddering and shaking that last just a few seconds. Soon as the engine runs for a TINY amount of time, it goes away. If I keep the engine running, or occasionally rev it while sitting still, it is fine. It's only if the ICE is off for maybe 15 seconds or more, that I have the problem again. (Just spitballing on that time.) The check engine light has not come back on all day. (I drove for hours, as I am a rideshare driver.)

My brother (who is our well-versed car guy in the family) is stumped. Someone had suggested piston rings, but he said that was not likely. I could not talk to the mechanic at the end of the day, as his shop closes at noon Fridays.

Anyone who can make heads or tails of it gets a free beer or five if we ever meet.

 

You need to remove the spark plugs and look into the cylinders. Likely #'s 1 and 2 pistons
are a bit cleaner than the other 2.
You probaly have a leaking head gasket. How is the coolant level?
A leak down test should confirm that.
While the engine is off, coolant is leaking into the cylinder(s), thus the rough start.

 

EGR cleaning way overdue. See first link in my signature.

 

A lot of what I had been reading seem to point to the EGR system. I had already mentioned the head gasket to my mechanic, but he didn't think that was the issue.

When I go take the car in Monday, I will mention both of the possibilities mentioned in the last two posts. Maybe one of those will point him in the right direction.

I will go out and Eyeball the coolant level later today. However, I want to think the last time I glanced at it, it looked pretty normal.

 

I think there’s been a lot of pointless plug and coil changes on third gen: code says misfire, mechanics go for low hanging fruit.

with your miles, assuming Exhaust Gas Recirculation cleaning not done, and the code saying cylinder one, classic symptoms.

 

Given my personal experience has just recently with trying to fix my 3D printer, my washing machine, and my furnace, I really don't blame people for going for low-hanging fruit. Fortunately, in the cases I mentioned, the low-hanging fruit was not the problem in only one situation.

My mechanic doesn't have a whole lot of experience with hybrid cars, but EGR isn't exclusive to them, of course. I wonder if he just didn't think of that off the top of his head. He has been quite open to suggestion, so I'm definitely going to mention that first thing Monday morning.

 

And I'm curious about the EGR and the particular behavior in my engine. It doesn't seem like it would be the kind of thing that would only cause the shaking and shuddering on initial start up. Based on what I know about it - which admittedly is not a whole lot - it doesn't really seem like it's the sort of thing that would go away quite suddenly shortly after the engine starts up, and would continue to affect it as it runs.

Quite obviously, the lot of you in here know a lot more about it than I do. If any of you can explain the physics and other science bits behind it only affecting the engine in initial start up, I would find it quite fascinating.

 

My understanding is that this happens on startup when there is residue(coolant?) in the cylinders, that accumulate when the car is powered off. Which is why you are asked to check the coolant level.
Based on what I have read on this forum I would prioritize resolving this issue to avoid engine damage.

 

That makes sense. It would seem that if the engine is stopped for just a short amount of time for instance, at a long red light, there could also be accumulation. It happens then, as well. The engine doesn't have to be off for an extended period of time for it to happen. Long pauses allow it to happen, as well.

With more insight into this, I am definitely not driving the vehicle. It is going into the shop tomorrow morning. I stayed off the road entirely yesterday. Today I have an out-of-town road trip, but we will be taking it in my other vehicle.

 

And I'm a little slow this morning. I haven't had my coffee yet.

While I was in the shower, I realized we've only heard from the head gasket/coolant camp. For the folks who think it could be related to an EGR system that needs cleaning, what could cause that when the engine is cold, or when I pause at a long a red light or for some other reason?

 

My 2 cents: the EGR and head gasket issues are hand-in-glove. Toyota engineers were trying to eke out a little more efficiency, and an EGR system helped with that.

I don't understand how it works, but my understanding is it HAS to work, and if it clogs one of the likely consequences is head gasket failure.

To corroborate this: the final leg of EGR passages is these small capillaries in the intake manifold, one per port. They tend to clog up with carbon ununiformly, clogging first at cylinder one. And that is where the majority of the head gasket failures are happening, at the adjoing wall between cylinders one and two, and the code coming up is P0301 or P0302.

If your head gasket is on the way out, a belated EGR clean up will not reverse the failure. The head gasket needs to be addressed first. For that, leak-down test and boroscope inspection is good. But EGR cleaning should be done right after, to avoid a repeat.

 

If I've said it once, Ill say it again... Miracle Whip is NOT mayonnaise!!

Oh, and your head gaskets bad.

 

I’m just finishing up with this now. Pull plugs look at all ceramics maybe in morning . We looking water droplets on no2 especially maybe a fine mist . I touch my finger to ceramic then to tounge . Ahh coolant .. it’s time for decisions . And they’re all costly . I wouldn’t keep allowing the car to clank clank in between on and offs it cannot be good on coupling plate or trans all possibly serious damage points if left to do this. IMHO only. Uhh good luck . I went with JDM engine And trans to try n curb hi labour and shop Times here in US .im at 1740 cash now engine is in and it starts and seems to run just a few kinks . MY car sat a year .