Misfire Cylinder 4

I don't understand why you don't listen......
Spark plugs go bad, some were where when they were made.
The ngk plugs took over 1000 miles before going bad.. They were new, from autozone...
Even if you have bought them from Toyota, one or more could still go bad...

You had the coils out. It's only one more step to swop the SPARK PLUGS.....
Why do you not want to swop them? Are they stripped out and you don't want to mess with them???

Other than the head gasket leaking, and the wiring you said you checked, the plug is the last thing....
You are more than welcome to just keep dragging it out though.....

 

Get another gauge and retest. Low compression would cause intermittent misfire. As the engine heats up; ignition in each cylinder becomes easier, because of all the heat generated. It's like having a roaring camp fire, where you just toss wood in vs trying to start a camp fire with wet wood. If it is in fact low, next step is to determine where it's leaking; past valves, rings, or head gasket. Bore-scope the cylinder walls to determine ring leak, pressurize the cylinder and listen to intake and exhaust manifold for leaks with a stethoscope. A more comprehensive test would be to disconnect the intake and exhaust manifold and inject smoke into the cylinder to see if anything rolls out of either manifolds. If the cylinder was totally dead, no compression - you may be able to see the burnt valve with a bore-scope.