Idle issue after Gen3->Gen4 engine swap

Hello,

I recently did the engine swap procedure on my 2011 Prius. The car runs and drives, but when idling or pressing the gas pedal when in P the idle is unstable (it sounds like you're lightly tapping the gas pedal repeatedly).
When driving, I didn't notice this behaviour flooring the gas or under normal acceleration, but the engine is pretty quiet when normally accelerating anyway.

The engine was taken from a 2016 XW50 and the engine code on it is X2ZR-Y22. The mechanic also had to replace the thermostat housing with a 16331-37100, because the one on the new engine didn't fit.

As far as I know, they reused everything from the old engine, including the EGR. Or at least I pretty clearly told them to.

What would be the cause of this issue? How to fix it? Is driving the car like this a stupid idea, or just a minor annoyance?

 

Would that be the cause? As far as I know, they modified the Gen3 EGR and installed it.

I know that using the Gen4 EGR can cause problems, but I didn't find anything actually detailing what kind beyond the vague claim of "driveability issues".

 

Funny that you mentioned this, because there were a multitude of issues with the shop, and the whole process took around three months because of that.

I should probably mention that there was a transmission issue (DTC C2303) which another mechanic managed to fix by straightening some pins to my understanding.

Anyways, for whatever reason, the hybrid battery actually got discharged during the engine swap and the car didn't start even after fixing the transmission. They charged the cells and it starts now, this being the only problem that remains.

I'm interested if the car is drivable like this without causing permanent damage, while I try to sort out this problem because in the long run it probably won'g be good, even if it was a minor issue.

 

Okay, thanks. I'll update this thread when I get the issue resolved.

 

Quick update about the car. I did another quick test drive, but after a while of driving home I get a check engine light. The engine also warms up way quicker than it did before the engine swap, in just a couple of minutes of driving.

I checked the DTCs with a reader and the code in question is P0401. Supposedly EGR flow is insufficient.

I also checked fuel trims while in P and pressing the gas pedal lightly, STFT showing 20% and LTFT 8%.

Could it still be a vacuum leak or is it something else? Is the car safe to drive, now that there's an actual DTC? To my knowledge, you can usually drive around with a yellow CEL, but given that the engine in the car is not the original, I don't know if I should trust it.

 

I'd say the shop is in the middle. Not a dealership (they'd probably say hell no) but not someone's garage with power tools either.

Here are the images. If they suck, tell.

 

Also a video of what it sounds like. The gas pedal was pressed at one point in the video.