Is that something I can further diagnose or worth getting into attempting a repair?
Or consider it acceptable for a 23 year old car with 180k miles on it and keep riding.

 

Pull the plugs on both cylinders, make sure that 2 has both valves closed, piston at TDC, put some air pressure to it. Do you hear/feel air coming out of the plug hole on 4? If so, that's a problem, and needs fixed.

 

That only works if both valves are closed in both cylinders. If either valve is open in #4, the air can escape through the valve, just as easily as it could through the plug hole. Removing the valve cover and loosening the rocker arm shaft would definitely close all the valves, making the air pressure test much more reliable.

 

It probably also depends on how bad the leak is..... But yeah, puling the cover and loosening the rockers would make sure you get an accurate test.

 

Spent the day checking pressure in the cylinders and am fairly confident it's not a leaky head gasket. 2 and 4 were pushing 130 psi and 6 was pushing 140 psi. I couldn't detect any leaking between them when pressuring one. Cylinder 2 fires strong.
It also wouldn't explain why at time cylinder 3 is involved in not firing. Currently 3 is doing well and it is only 4 not firing.
I keep looking for a vacuum leak and not finding any. I tried cutting off and dead ending EVAP and HVAC and no change. I'm confident in spark and fuel.

 

Even at 130 that should be more than enough compression for the cylinder to fire properly... If you are getting good spark TO THE PLUG, and fuel.... that leaves mechanical issues..... but compression is at least passable....

What plugs are in it? Might try swapping plugs around, see if the misfire follows the plugs.

 

Don't know where you bought the plugs, but if they came off ebay I have seen lots of things about cheap ebay knock off plugs that don't work well.

 

It has the OEM Champion Cooper plugs in it. Got them from popular zone based auto parts store.
I've moved plugs and wires several times trying to diagnose and never moved the misfire. This behavior started with cylinder 3 and intermittently over weeks switches between 3 or 4 (or both) not firing at idle and throwing codes.

 

plugs seem good enough

 

How old? Also, cap and rotor? How old are the wires??