Rattling 2k miles after HG replacement.. but only after sitting 5 mins.

2013 Prius. Replaced the HG about 2-3k miles ago @ 142k miles. Everything was kosher, until recently.
When the car sits overnight or more than an hour, no startup rattle.
When I drive the car, turn it off for about 5 mins & turn it back on, engine rattles. Initially thought maybe something in the fuel pump was bad, so I just replaced the entire assembly with an OEM unit - still rattles.

Intake manifold cleaned, EGR circuit cleaned, injectors were sent to be rebuilt / balanced, new plugs (original coils), new gaskets, headstuds, head machined, block was checked for flatness (0.05mm feeler gauge). Engine runs great otherwise. I do about 1500-2000 miles a month at about 90% highway and it runs great. No coolant loss detected.

Two things I still need to do - replace evap solenoid (sticky?) & refresh ECU to the latest firmware per T-SB-0041-15.
I also read one situation on reddit where someone's catch can tubing was too large, so it would sporadically rattle for a few seconds until vacuum was built. Currently sourcing an OEM PCV tube to rule out the possible catch can issue.

Any other suggestions? Sticky EGR valve?

 

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If I start it and immediately drive before the engine starts, I don't really get a rattle. I can't tell if it goes away when I rev it, since the rattle is short and stops within a second. Also, if you're facing the engine, it sounds like the rattle is coming from the right side of the motor where it interfaces with the trans. No CEL.

May be related - when I first changed the HG, I would get a weird half second low idle as shown in this video - which led me to believe the fuel pump assembly needed to be replaced.

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Yes.

Everything was actually torqued to FSM specs, i'll check again. If something was loose, I would imagine it would rattle regardless? (cold/warm). I have let it idle for 10-15 mins with maintenance mode, no shaking unless I stop it and let it sit for the 5 mins & restart. Seems like too short of an interval for coolant to seep into the chamber.
If it was a HG leak, I would imagine it would rattle in the morning on cold start?

Techron has been run thru the tank, but I've replaced most everything in the fueling system.. new OEM pump, injectors cleaned/balanced, head hot tanked, carbon cleaned off pistons. This one definitely has me scratching my head.

Intermittent coilpack, maybe sticky evap valve? It seems like whatever the issue is is when it's "warm", since the problem disappears after more than an hour.. In any case, I bought a coolant exhaust leak tester to test.



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I bought the car with a leaky headgasket, but repaired it as soon as I got it. Seller said it never overheated, just would rattle in the morning. Toyota borescoped and confirmed coolant in cyl #2.

I haven't borescoped the cylinder but that'll be next, probably along with a leakdown test.

Confirmed there was no warping in the block with the straight edge & feeler gauge.
Here's a video with the car starting up after I let it sit for an hour. Small shaking seems normal per other video's I've seen?

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All gaskets were changed - EGR circuit gaskets, valve cover, spark plug seals, injector O rings, valve stem gaskets, water pump & gasket, exhaust gasket, throttle body, intake manifold, crankshaft seal, etc. I used the Fel-Pro HS 26515 PT-1 gasket set, and additional OEM gaskets that were better quality over the Fel Pro.

 

~139k

 

I have not, gonna look those up.

The video I posted is my car,
(same car that was rattling in the previous video), only difference is I let it sit for an hour and started it.