Faulty EGR Valve? New HG, OCC, clean IM, EGR, etc...

Good morning everyone, I'd appreciate some feedback on a really small but annoying issue I'm running into after having done my Head Gasket (HG) on my 2013 Prius (235k) that's really annoying me.

TL;DR - Car has a new HG, Water pump, thermostat, Oil catch can (OCC) installed, crystal-clear EGR system and twice-cleaned IM, no codes being thrown whatsoever, idles like a dream and runs great under power. Car shudders noticeably under low load (sometimes to the point of physically shaking the frame), and following a Gasket Masters video, this issue went away upon unplugging the EGR Valve. Is the valve just shot?

Context:

Around August this year my car began to give me the morning death rattles (which upon initial investigation immediately lead me down the 'HG FAILURE' rabbit hole and sent my wallet running for the hills.) It was around this time that I noticed that my coolant was low, so I did what any man in denial would do and topped off the coolant and proceeded to look down other avenues which could have explained the misfires and rattle.

This lead me to the EGR rabbit hole, which I hoped and prayed was my issue. My first line of defense was cleaning out the EGR and IM to help troubleshoot the misfires, but I was unfortunately only able to get the IM clean with the limited time I had to take my car apart (the notorious EGR bi*ch bolt brought the cooler cleaning to a grinding halt.) I also took the time to replace the PCV valve, Spark plugs, Coil Packs, and all necessary gaskets with the car torn apart.

As you might have guessed, this didn't solve the looming HG issue, so I began doing my research for all of the necessary parts and repair manuals I'd need to complete the job myself.

Thanks to you lovely people here on the PriusChat forums, I was able to get all of the necessary manuals, parts, and technical know-how to complete the job at home over the course of about 10-days working off and on. Both coolant systems were drained, with the ICE side getting flushed completely prior to dropping it entirely. I also drained and filled the transmission fluid, which hadn't been done for the life of the car to my knowledge. Timing system was completely replaced (save for oil pump chain since I wasn't able to get off the sprocket), timing marks were triple checked, and the tensioner was properly deployed upon timing cover install (with a full-engine revolution completed to confirm for good measure.) Water pump and thermostat are brand new, OCC was installed to prevent oil from pooling in the IM, and the EGR system was completely cleaned out until it looked like it was fresh off the factory floor. Reassembled, added new oil and filter, and topped off the coolant.

Upon reassembly and start-up, everything was running smoothly and she was purring like a kitten. Idles sounded clean, no more death rattle, and I waited until the cooling fans started up to ensure proper coolant level. Revving her in maintenence mode gave me zero cause for concern as it sounded great and didn't hesitate in the slightest.

Fast forward to doing some actual driving with her on the road and I couldn't help but notice a very subtle shudder when she was under light loads (think the Eco-section of the hybrid indicator, not the power section.) This shudder was only present under light loads on her engine and immediately went away with more power. I tried to isolate the issue by rolling down big hills without any power but the issue only ever was present under low loads to the engine.

Heading back to Google, I finally got a hit on an issue similar to my problem with this Gasket Masters video (

). I parked the car not too far from home, shut it down and unplugged the EGR Valve, then started her up and drove home: no shudder.

So here's my conundrum: if everything else in the car can be assumed to be functioning properly, all EGR system/IM parts are cleaned out thoroughly, and the issue disappears without a functional EGR valve, would that leave the EGR valve as the final culprit?

This is really the final hiccup in my car, thank you in advance for your input.

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On a related note, I'm about 60% complete with my DIY 2013 Prius HG guide that contains all necessary steps and procedures to do the entire job yourself. Once it's complete I intend to upload it here along with the many photos I took of my journey into the engine, along with some things I would have done had I known/remembered to do them.

 

That's what I'm afraid of, uneven flow into the intake ports. Might need to take apart the intake tomorrow and shoot some distilled water through the EGR intake pipe to see how each passage flows.

What do you mean by rut? I can take it apart here in a couple hours and post pictures here of the guts. Can't get to the EGR Valve itself without dropping some coolant and my neck says no go for that job today lol.

 

Looks like my account isn't old enough to post pics. No I do not see a rut.

Here is the inside of my rotor. It's supposed to thread and unthread on that spring, correct? (I have more photos if needed.)

 

Far as I'm aware this is the stock EGR that came with the vehicle. Where are you seeing a difference in the images?

Here are the remaining images. Keep in mind this EGR Valve was working flawlessly (to my knowledge) prior to doing my HG job. I just took it for a drive tonight and had my girlfriend monitor the EGR on the OBDII Scanner and it was performing as-intended as far as we could tell and the shuddering only picked up when the EGR Valve was open. The car drives crystal clear when the EGR is closed or unplugged.

 

So I was discussing the issue with a coworker and he had an idea that sort of threw me through an epiphany....

Prior to doing my HG, the EGR had never been cleaned and it was incredibly plugged up upon removal, like you could pour water into it and watch it slowly drizzle out the other side after a couple minutes. Attempting to blow air through it was like trying to breathe through a coffee straw.

Is there some kind of "learning" the computer needs to do to compensate for a cleaned EGR? Assuming the EGR Valve itself is working properly and all of the Cooler and Intake passages are clear (will confirm that later tonight), what if the computer is still programmed to run the EGR in it's previously clogged-state and it's overcompensating with exhaust gases?

Might be overthinking it. Let me know what you think.