what are some possible symptoms of the intake valve carbon buildup

[fastboatster]

This might have been asked before many times but I would like to double-check this again. What would be the symptoms indicating that the intake valves need carbon cleaning? I thought my new to me engine had an okay carbon buildup which probably could be left be for the time being, but then I saw some YT videos where people had just about the same amount of buildup as I do and that was causing issues for them. I'm getting about 5 or 6 misfires in 2 or 3 miles, wonder if this could be caused by carbon buildup. Already got the new plugs and coils.

[bandit]

cold start misfires

[Robdukes]

How are your cats? Mine need replacing/removal and I'm getting misfires from that.

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[fastboatster]

I reused my old cats with the replacement engine. The worst of my 2 cats looked like this:
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another cat looked similar but the "beehive" structure was completely flat and looked very nice. Both cats turned out to have some sharpie markings on them, probably from some salvage yard and probably have been replaced at some point already, there's no way stock cats would made it past 150kmiles. The engine feels great when on the throttle, I just feel some vibrations at idle. I think what I'm also getting is when I stop, the rpms stay at 900 rpms for a second and then they go to normal. I don't recall it too well but I think the same started to happen with a deceased engine, too, after I did dual clutch replacement. My current guess is that the brake booster hose is either not connected properly or got damaged somehow, it had to get disconnected because I had to remove the false firewall to access the upper bellhousing bolts.

[fastboatster]

Okay, the car told me today it has an evap leak, it threw a P045600 code. That might explain some of this. Now need to figure out how to find what’s leaking in the evap system.

[fastboatster]

Okay, it definitely had something to do with evap valve and rubber lines. I initially just wanted to install the purge valve which came with the new engine but it became clear that the old rubber lines are in a really bad shape. I.e., even when clamped, they would rotate very easily around their fittings. This was especially the case for the fittings secured with oetiker style clamps. The old line was very brittle as well. Bought some fuel injection hose and replaced the rubber parts:
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Idle has improved a lot, to the point that I can barely feel any vibrations anymore. Will need to drive the car more to get all the readiness monitors completed to see if there’s anything else not working correctly.

[fastboatster]

spoke a little bit too soon. The next day, still got some vibrations at idle after the cold start, drove for a few blocks, feels smooth again. drove some more, started to get vibrations again after getting hot. Was also watching misfire counters, no misfires at all when cruising but it starts to get some when accelerating (even not wot and at when accelerating to 3k rpm), not even noticeable from the driver's seat. so far, we got both cats and one exhaust manifold transferred over from the old engine and reused an evap check valve from when I was replacing the evap hoses and purge solenoid. I also got a used supercharger off eBay, perhaps this pos also has leaking cores. Will have to pull that thing out and check. It will be "awesome" if it's leaking.