4.0 1GR FE intermittent misfire P0304 ( not plugs or coil)

Please help, I know this is a 2nd gen forum but I also know you guys are experts on these motors.

Vehicle- 2012 4Runner 4.0 1GR FE
155k miles, daily driver, well maintained. History of rodent damage.

Problem- Vehicle threw a P0304 misfire cylinder 4 code with flashing CEL and was running rough( active misfire)
Put new Denso Iridium plugs in all cylinders and replaced #4 coil with new Denso coil.
Truck ran great for about 25 miles, then it threw the exact same code with the same symptoms. Moved coils around and confirmed it was still cylinder #4 misfire. Cleared the code and it drove ok with the exception of a couple misfires while rolling to a stop but not enough to throw a code and make the CEL pop up.
I took it to another shop and they drove it nearly 70 miles before they got it to throw a code again, P0304.
They claim it’s a valve issue because they checked compression and the compression is good, but saw fluctuations in the vacuums.
They recommended to pull the heads and service the valves at a cost of $8k
Both shops couldn’t find rodent damage and both confirmed good compression.
No backfires or any other symptoms have been noted.

My questions are-
1) what steps would you take in further diagnosing or troubleshooting this vehicle?
2) Could a valve issue cause this type of intermittent misfire?
3) Are these motors known to have valve problems?
4)What do you guys recommend in general?
Thank for reading and any helpful advice is greatly appreciated.

 

I'd put some OEM copper plugs in it and see if it helps.

If misfire continues a decent backyard way to check for a valve problem is to hold a margarine lid against exhaust pipe and see if it gets sucked against the pipe for a split second. Paper works too

 

Swap the spark plug too. Some are duds right out the bag or quickly fail…

how does the spark plug well look? Any oil? You could just have a valve cover leak…

The 2015 MY is known to have some valve issues but not 2012 and not at that mileage.

Don’t pay $8k to have the heads serviced. If all else fails, you’d be better off swapping in a low mileage motor.

 

You can buy a new short block for 5K, never mind valve job for for 8K. Lol

 

It’s more likely a head gasket than a valve, but both jobs are similar.

A good borescope in the cylinder can detect both. I’d be looking in the cylinder with the coolant pressured and inspecting the valve faces.