Cylinder 4 Misfire

I am struggling to understand why I’m experiencing a misfire. It only occurs on a cold startup, and after a few seconds, it runs completely normally. After a couple of days of doing this I got a flashing cel and then it showed up with P0304. the traction control lights come on, but it still ran normally a few seconds after starting. I replaced the cyl 4 plug and coil, but after a couple days it started doing it again. It worries me that it could get worse, even though it drives fine for now. It has 114,000 miles, so why is my toyota breaking down. Has anyone had this issue?

 

I hope I'm wrong but it sounds like a blown head gasket, early 4th Gen V6s are known to have bad head gaskets, and usually it blows around the #4 cylinder, any 4th Gen V6 with a build date before 12/05 have the earlier head gaskets design and can on some V6s fail, after that date the V6s have a new designed head gaskets, any early build 4th Gen that have had the head gaskets replaced should have the new designed gaskets.

What is probably happening is once you park it some coolant leaks slowly past the head gasket into #4 cylinder overnight, when you start it the next morning it misfires until the coolant is burned off then it runs fine.

The build date is on the VIN sticker on the driver's door jamb.