Yes it shows leakage at exhaust but it’s borderline passing. And I think I’ve said it before- the car runs too good for a serious exhaust valve issue.

plus now given the fact the AC being on has stopped the misfire is puzzling. I’m looking at every option I can that could be the fix.

 

I thought I had explained that.
The way misfires are detected is by measuring the variation in the revolutions of the crankshaft. The AC compressor puts a load on the harmonic balancer which would reduce vibrations of the crankshaft. A "slightly burned" exhaust valve will cause some vibration, along with damaging the cat. The vibration in the crankshaft manifests itself as a variation to the crankshaft sensor. The computer knows which cylinder is firing at any given point in the crankshaft rotation.

Therefore running the AC could turn the detected misfire off, The CEL is set after the misfire is detected in the second consecutive ignition cycle.

P03xx only causes a CEL: when it is severe enough to potentially damage the catalytic converter. The reason the code would cause an emissions test fail.

 

so slight update. i changed the motor mount (one on pass front side). no change. i shut the AC off for the first time in months and the first 2 restarts in popped the CEL.

now i am wondering if i should be doing the timing and balance chains. there is no way to check the balance chain is there? its hidden behind the timing chain I believe.

 

Not hidden but behind the timing chain.. Have you checked the harmonic balancer and its bolt?
You still don't accept that burned valves can cause vibration or variation in the RPM?
Maybe experiment by taking the serpentine belt off and see what happens.
P0304 only lights the CEL on the second consecutive ignition cycle that it happens the first time it will show as pending, I thought I had explained that also.

 

yes I get the 2 starts. that what I was saying before it seemed to be almost random, however now it the very first 2 starts without the AC on, first pending second code

and yes I understand the burnt valve could cause the vibration hence the CEL. but before I send the car off to scrap yard I'm trying to try any other alternatives.

one other thing I have been thinking- and I'm a little hazy here and its been almost a year. but I swear when I first got this car the PO had been battling a P0303, and then it suddenly switched to P0304 for me. This is what had me thinking about timing and balance chains. a burnt valve couldn't magically switch cylinders. also theoretically here, but a stretched timing chain could be causing my exhaust valve to be closing late couldn't it? also adding in the car is at 95,000 miles so it could be due for a chain.

 

You said all cylinders had signs of "marginally burnt valves"; do you think maybe, one could get worse than another.
If it is a matter of coking on the valves there is a chance a good Seafoam burn might help. I do know that I did a top clean with seafoam that did free up the oil control rings.
A stretched chai would cause all of the valves to go wonky, not just 1.

P0304 is saying "the crankshaft rotation speed is different at the moment cylinder #4 is supposed to be in power stroke from the rest of the time". Like as if combustion product were escaping from the cylinder when they are supposed to be pushing the piston down. The AC compressor is stealing some of that rotational energy, evening out the stress. Maybe.