Dreaded Misfire

Good morning, I'm new to this forum. Red seal technician of 35 years.
My son bought a 2012 Tacoma 4.0.
Drove it home. Next morning rough running and misfire. Engine light flashing.
Of course my first reaction was with high kms just do regular maintenance. Plugs and coils. Erase code. Drive truck for quick drive. Seems to work fine. After a few drives, same thing. Misfire. Light flashing. Learned quickly of 2 trip logic and ecm shutting down cylinders as to not damage converter. Noticed whenever sitting over night first start would be rough. I suspect leaking injectors. They are cheap so I replaced them all. Like I said high mileage (300k)
Erased codes. Truck started great. No misfire counts.
Son took it up the road possibly 6kms. Filled with premium fuel.
Returning home Engine light started flashing and of course misfire.
I'm getting empty of ideas. Possibly low fuel pressure?
Any feedback would be great. Thanks

 

Spark plug tube gaskets, maybe. Welcome to TW and good luck!

 

Not that.

 

Head gasket leak.

What did the spark plug look like? Wet?

Coolant getting low?

If it's the head gasket, get the copper flakes in a bottle.
With the engine totally cold-
Remove about a half gallon of coolant
Mix the sealer with the half gallon of coolant. And put it back in the radiator.

What the stuff does is clump up and melt together when it gets hot.

The first place to get hot is usually the leak, so it clumps up there.

I work on a lot of cars and people are generally idiots because they refuse to read the directions or understand how an engine works. These morons pour leak stop right into a hot radiator and then say "this product killed my car".

Anyways, you get the point.

Off topic, but the truck takes a few hundred miles to benefit from high octane fuel. After that, I can get maybe 20-30 more miles per tank from 93 compared to 87. Not exactly worth the price difference, but going 230mi is much better than going 200mi.

 

It runs rough on cold startup because a little bit if coolant leaking into the cylinder(s) overnight. It chokes on the coolant for a few seconds and then smooths out. I'll bet you have a gradual/slow loss of coolant too..

Sounds like a head gasket leak