Any mechanics that can help diagnose this?

I have a 2011 Prius. A month or so ago I got a P0301 code and replaced the spark plugs and ignition modules. It ran fine until today when it started misfiring again and again I have a P0301 code. I’ve also noticed that while in Park with the gas to the floor the RPMs rise and fall while my foot stays hard down. I also noticed an ethylene smell in the cabin when it started misfiring. Also, starting from a stop it misfires a bit, but once up to speed it’s fine. Before I start going to the next thing I can think of, which is to clean the intake manifold and EGR valve, do you think that would even be the issue? If not, then what?

Edit: it only misfires for a few seconds before going quiet again, even just sitting in park

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DownTheStreet · 56-60, M

@Zaphod42 I don’t know how the Prius engine is laid out but check the ones you’ve put in since. You’re sure of the basic stuff like the plug wires being in damaged and connected firmly in place at both ends? Does it misfire at all rpm ranges?

Zaphod42 · 51-55, M

@DownTheStreet It’s only misfiring when the gas engine first comes on. After a few seconds it levels out, or if I’m at a stop sign or light it’s misfires when I first accelerate, but then levels out as I pick up speed.

I’ll check the plugs…I just hate to have to take out the wiper assembly and cowl again, lol

DownTheStreet · 56-60, M

@Zaphod42 plug wires fine? Just trying to eliminate the easy cheap stuff.

Zaphod42 · 51-55, M

@DownTheStreet Near as I can tell they’re ok. It’s a wire harness, so I can’t see the length of them, but they’re fasted securely anyway

GeniUs · 56-60, M

@Zaphod42 Quick trick I found by accident; run the engine with hood up in the dark, any shorts/cable problems show themselves (blue light /sparks). Just a quick way to spot anything like that but does not guarantee that the cables aren't faulty. (If that makes sense).

Zaphod42 · 51-55, M

@GeniUs That makes sense! If I don’t have this fixed by dark I’ll try that