Rough thuddy startup, like piston rings are carboned, happened before and after HG replacement

2015 Prius V 5
173,400 miles

Video recording/audio in the cabin to see the shake (will continuously replay after two turn ons unless you pause)

Audio recording in engine bay if you want to hear it, Vocaroo: https://voca.ro/1odpnLSIPpnE

When the ICE starts it's an instant rough thuddy start at first for half a second then it's somewhat smooth after. Obviously you can't hear the feeling of a thud but it's hard. Been doing it for 7 months or so, happened before and after a head gasket replacement. Cutting off it's a little less.

Had the head gasket replaced just recently a week ago after it was banging around with a "misfire cylinder 4" code, first place said they found carbon in the coolant, coolant in the cylinders, head gasket needed. Second place said the plugs were fouled and did need a head gasket definitely.

The guys who did the head gasket (Gasket Masters) also cleaned out the EGR and replaced the EGR cooler with another clean one.

Since maybe 7 months ago she was rough starting just the same as today, back then figured I'd look in the throttle body, and there was a greenish/brown colored liquid pooled there, maybe a few tablespoons worth, smelled like gas but then again I had sprayed cleaner in there. I've found other similar posts about liquid pools being found but they say it's normal..

Oil in Throttle Body: Normal? | PriusChat

Other than that I've been told I'm burning oil, only because they heard me say there was black soot all over the back, and the weird thing is the oil is always level, even after 5k miles. Since I bought the car at 145k there's been a tremendous amount of black soot coating the rear of the car, like the entire rear. You swipe your finger just a few inches and it's like you used a large black sharpie. This collects over the period of maybe 2-3 weeks then I wash it off. The picture enclosed is after I washed it a week ago. I see other Prius V's driving around and many of them have the same thing, thought it was maybe normal for them. So, after the head gasket replacement telling them this the guys told me to put 1/3 bottle of seafoam in the oil right after an oil change and ride it throughout, that after 3 changes I should see much improvement, except the instructions say no more than between 100-300 miles ‍♂️, but I put in a little less it's 6.6 oz maximum for the 4.4 quarts of oil I have per instructions, 1 - 1.5 oz per quart, unsure about this I get other posts saying you shouldn't leave it in for long or other parts might get coated with carbon mixed stuff that weren't originally coated. What's your take on that I mean these guys seem to know what they're talking about.

So a few days ago I put 5.3 oz of seafoam in the oil going on around 60 miles now, seeing a small bit of improvement it's not as rough at idle as I remember, but I did smell seafoam coming out of the exhaust starting yesterday, several days after putting it in, which shouldn't be happening I presume.

Yesterday I also put in just under 12 oz of B12 Chemtool in the 3 gallons left tank and filled it up topped off with 8 gallons. Hopefully that cleans up some more. 11.9 gallons, 1 oz per gallon if under 15 gallons per instructions.

Thinking about getting this other product I heard about from Scotty Kilmer, looks very very promising it's called 505 CRO for the engine oil, 505 CRF for the fuel, just pouring it in and it gets rid of carbon.

Weird name because I have about 1,000 Cro on crypto. com. Anyways

So my initial instinct smelling it coming out of the tailpipe is worn piston rings / blowby, but another is timing. Coils not so sure.

To be clear I smelled it coming out before I put in the B12. And actually it wasn't continuous, it was only maybe for a few minutes then it went away, so what could be dumping it into the combustion chamber like that? Or just coincidence of uneven rings.

It's quite a thud at times, feels like whatever this is happening may be why cylinder 4 misfired and plugs were fouled and potentially never needed a head gasket in the first place. Fouling my plugs I installed only at 155k miles, just around 18k miles ago with Denso pre-gapped iridiums, it's at 173,400 now with Autolite iridiums, said they last much longer, cheaper too at only $9.

I'm afraid this fouling may happen again, causing another misfire.

So, your thoughts. I already touched a little on this with another post but I wanted to make a new one so possibly more/other experts can give their take specifically on this instead of just, why is my car misfiring.

 

Any takers?

 

It's an abrupt shake it's not normal I want it to go away without spending $3800 on a new engine or using a warranty after neglect. Read that last bit at the end of my post too hah

 

I told the guy everything I said here, he said he thinks it's burning oil, but the thing is none is being lost from checking, like nothing.

I check the level every few weeks, not a slight movement down the stick from exactly level. I mean for that amount of soot collecting on the back without being oil the only other thing it can be is there may be oil collecting elsewhere over time behind the throttle body and burning later, or it's gas, bad fuel injectors, incomplete burn. I mean thinking about it more it could be for every start up, hinting around the fact that it bucks alive for the first few turnovers. Maybe cylinder 4 has a bad injector? Not enough spray but enough to flood it over time without it firing then it all finally starts and comes blowing out of the tail pipe... ? Whatever is going on it's fouling my plugs from what they told me, the plugs were fouled at 18k miles on them. I'd expect at least 30k out of plugs if not more

 

Like what

 

Someone else was having this same exact issue in 2019 and they solved it by replacing the Coil Packs. That's my next job. How much are they?

Post by solved poster:

Knocking/bumping when engine turns on/off | PriusChat

 

The Coil Packs.

Knocking/bumping when engine turns on/off | PriusChat

 

The Coil Packs.

Knocking/bumping when engine turns on/off | PriusChat

 

Coil Packs may be the answer. 2019 happened to this guy, he solved it

Knocking/bumping when engine turns on/off | PriusChat

 

Coil Packs

Knocking/bumping when engine turns on/off | PriusChat

 

Got Dang. $121 per coil. $534.52 if ordered in by Toyota.

Part number: 90919-02258

 

The guy didn't get misfire codes constantly. Interesting

 

eBay's got it for $91, all 4 of them. Total $91 after tax, shipping. $91. Screw $500. Genuine OEM, Denso, original. The real stuff. I'm proud really. 4 days shipping.

 

Also while mine was misfiring, it wasn't getting any codes either. It had to be connected. These Prius's aren't sensitive enough