Cold start cylinder 3 Misfire issue ( long running issue, even longer post )

[Furly]

is the head really "brand new"? or is it just new to you?
if there is no code stamped on the front where it should say AMB/AEB etc.. its a chinese replica head. if you got a used head, step #1 is to have an engine machine shop leak test it to make sure its good, then resurface the sealing surface. inspect valve guides and replace valve seals while you're there. make sure you thoroughly cleaned the block's surface as well. and inspected for flatness.

[Dangerb]

is the head really "brand new"? or is it just new to you?
if there is no code stamped on the front where it should say AMB/AEB etc.. its a chinese replica head. if you got a used head, step #1 is to have an engine machine shop leak test it to make sure its good, then resurface the sealing surface. inspect valve guides and replace valve seals while you're there. make sure you thoroughly cleaned the block's surface as well. and inspected for flatness.

The head is new to me. It's a low mileage AWM head that i had inspected, then i stripped it completely down and rebuilt with new seals. Valve guides were good. Myself and The tech who helped me swap the head cleaned the block surface. The only thing we didn't check was the blocks flatness

[Dangerb]

Update:
The weather has been dipping below the freezing point at night fairly often now, and every time my car has gone into the normal low idle on cold start, the car doesn't at misfire at all. Otherwise the car still misfires for a few seconds during high idle coldstarts if it has sat for 8+ hours.

Sidenote: I picked up a spare engine with forged IE rods ( among other goodies ) back in August and stripped it down completely for a full rebuild. The bottom end is getting bored, decked and assembled at the machine shop this week. I replaced the valve seals on my stock AMB head and will be swapping it back into the car and will have the AWM head that i'm currently using pressure tested and decked to install it on my newly built and painted block.

I've wanted to install forged rods for a couple years now, and learning that i have low compression on one cylinder has given me the motivation/excuse to rebuild an engine. I'm still not convinced a fresh block and head will fix the coldstart misfire issue though. I still want to figure out what the root problem actually is so i can be sure to fix it properly

[Let it snow]

Maybe your SAI system is causing an issue. It is active during cool weather with a cold car (high idle) situation .

[Dangerb]

Maybe your SAI system is causing an issue. It is active during cool weather with a cold car (high idle) situation .

I haven’t tested my SIA pump in Vagcom, but it seems like it’s working fine compared to previous ones I’ve had go south on me. Is there any possible way the SIA pump/ Combi valve could be causing a cylinder specific misfire though?

Either way I found an older troubleshooting post regarding the SIA from OldGuy that I’m going to try out tomorrow since it’s super easy. I’ll see if disconnecting the hose between the Combi and the SIA pump has any effect at cold starts.