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.

 

Or #4 Fuel injector

 

Cylinder needs spark, fuel, and compression to work.

Use a borescope and check injector wiring under the intake manifold for rodent damage - common on Toyota V- engines.

Do a compression check on cyl #4. Could be blown head gasket as AuSeeker says. Common on 2003-2006 and slightly less common on 2006-2009.

You got cyl #4 identified correctly? It's driver side middle cyl.

 

I would try to do a pressure test of the intake system all the way thru the throtle and see if everything there is ok. A little vaccuum leak or tear in any line there could give you a code hence the misfire. Check the MAF too and the fuel system while you are at it.

 

^Vacuum leak could generate a lean code (due to more air being introduced into the engine than have been metered by the MAF sensor), not a specific cylinder misfire.