2nd gen start knock but no codes for misfire

You could have a very small headgasket leak that lets a very small amount of coolant/or (sandy water?!) into a cylinder causing a rough start.

 

Blown motor.

go on you tube look up

Prius inspection

it will show you how to put the motor in inspection mode where it will continuously idle till you shut it off.
While running get under the car and listen to the bottom end.

 

At that many km with poor maintenance anything and everything is suspect. It could be a mechanical noise until oil pressure builds up such as timing chain slack or worn rod bearings. It could be anything marginal that IS causing a misfire, but not long enough or bad enough to set a code. If it's that poor of a condition, how much effort you want to put into it? I would do minimum basic repairs and drive until something gets worse (or dies).

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When my 2001 1NZ developed its occasional cold-start knock, it remained a mystery for the remaining years I had the car. Compression was fine and there was no loss or mixing of coolants, I had a few different experienced mechanics listen and say they were sure it wasn't anything bottom end, valve adjustment seemed sort of tolerable if not perfect everywhere, the #4 cam lobes looked a little bit like maybe less oil reached them, but nothing definitive there. There just never turned out to be any smoking gun, and in my case it never led to any more serious problem. It just remained a puzzle.

 

Not sure I remember exactly. Seemed more frequent in cold weather. Often enough it bothered me, but also unpredictable enough that I had several instances of not being able to make it happen for some mechanic I wanted to listen to it.

 

The symptoms you describe are consistent with the VVT Oil Control Valve where it makes a knocking noise of short duration when the car is started, but then goes away. This happens frequently in Toyota vehicles (many different models) that have not had regular oil changes and the valve gets gummed up. Eventually the solenoid dies from being overworked and a code gets thrown because the valve timing can't be changed at all, but if the noise occurs just at start up and goes away quickly you won't see a code. If as you said, the noise is coming from the rocker area it's worth looking at since it's easy to check and it's only a $20 part to change out. If the solenoid is still working well then just pulling and cleaning the valve could fix it.

 

Can you point me to more on this? It's an explanation I hadn't seen before and seems worth knowing about.

Are you saying the solenoid valve gets gummed up, or the vane actuator on the camshaft? Or both?

What produces the knocking noise?

What are you calling the $20 part to change out? The solenoid? (I've assumed the vane actuator is more than that.)

 

Right, it is usually the VVT actuator (cam sprocket) that has the problem. Specifically there is a pin that locks the VVT in "park" position when oil pressure drops. Wear or deposits cause the pin to not seat or lock. So on startup valve spring pressure pushes on the cam lobes as the cam turns, causing the guts of the actuator to jump forward and backward against the internal stops until the system builds up oil pressure.

Don't see this problem very often on Toyotas.

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Interesting! I knew about that pin (or at least inferred there must be something like it, from the compressed-air trick shown in the repair manual for rotating the actuator). This is the first I've heard this problem mentioned.

Is it something you've run into more often in other makes? Have you run into it on some Toyotas? Do you know of any articles, service bulletins, youtube vids, etc., that would have any more details about it?

 

I have seen a couple of times on older Honda 2.4L Accord and CRV- there's a TSB for it (# 09010) - you replace the VVT actuator (and I do the timing chain if it's worn enough). I also had a confirmed fault on a mid 2000s Camry 2.4, but that car was too overall tired to justify the repair cost.

It can be difficult to differentiate a VVT rattle from a timing chain rattle unless you pull the valve cover to verify if the VVT is locked or you have chain slop.

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G2 has a VVT oil filter right next to the solenoid to prevent this exact occurrence. Not sure if the G3 has a filter.
It will be a hex head bolt head.

I recently replaced my solenoid with a Red Bullet works really good.
Motor really likes the advanced timing and no pinging. Very peppy.

 

I'm not say it's the problem, but there's lots of history with Toyota cars with this issue. The issue exists on Scions, Camry, Corolla, Prius and others. Not a really frequent occurrence, but common enough for the symptoms you mentioned to be worth looking at.

My understanding is that the valve refuses to move from being gunked up and that leaves the valve timing at the last position it was at before shutdown and the solenoid can not produce enough force to move the valve in to the proper position until either the oil pressure increases from the pump or the oil heats up and the pump becomes more efficient. So the force needed to move the valve increases for a short time and the solenoid can't deliver enough force. This is heard as a knock from improper detonation in the cylinder, usually pre-ignition because the timing is now sub-optimal for a start. Once the oil pressure builds from a start there is enough pressure to at least come close to the demanded timing change by the ECU and everything is groovy again. But it might still be off, just not enough to throw a code. If it can't achieve proper timing changes you will see reduction in fuel economy even without a code, and as the problem gets worse it can be a significant fuel economy change. That would be another indicator of this issue, but might not be as easy to notice.

I suspect there is a delay in the engine start sequence where the ECU ignores the timing change values for a short time period, but if it continues a code will be thrown. I have no way to verify the algorithms used by Toyota and I don't think they published them, but after working on emission system programming for another auto manufacturer for many years, I suspect that to be the case.

BTW, this can also occur from a failing solenoid.

Take my opinion with a grain of salt, but the symptoms you mentioned at least warrant a quick check.

 

The entire part, valve plus solenoid is a single assembly you buy. It available on Amazon, even as a Prime item for under $20. I haven't check Toyota, so I would guess 5x that price...lol.