420A 2GNT Misfire cylinder 2 and 4

[MotherShip]

I have a 99' RS non turbo 420a and I'm currently getting a cylinder 2 and 4 misfire code (P304 P302) as well as a random misfire code (P300)
I just changed out the spark plugs and have them gapped out to .048 and also changed out the spark plug wires. This helped a bit but it's still running poorly.
I'm not too sure what else to check or what can cause this so any help would be great.

 

[97egl]

I would check compression and fuel pressure. Since it's 2 & 4 more than likely it is not an issue with the coil. Normally coil issues will be on 1&4 or 2&3.

 

[Nickolision]

i would check out the coil pack next, i had some misfire issue sorted with all those 3 replaced

 

[MotherShip]

So I checked the spark plugs and did a compression test and the numbers are still with in spec.
After that I went for another drive and maybe 5 minutes into the drive the check engine light went away and the codes aren't there anymore.
Today I decided to replace the valve cover gasket since there was a slight oil leak and after finishing everything up I started the car to check for any leaks and noticed a hissing sound.
After checking the valve cover for anything obvious I realized that it's sucking in air through the oil dipstick tube. With the dip stick removed the engine idle starts to slowly build up to around 2.5k rpm. When the dipstick is out I covered the hole with my thumb and the idle dropped back down to normal.
The dipstick seems to have a slight crack near the base of the handle but I'm not sure why it's sucking in air when the dipstick is completely removed.

 

[BLACK'98DSM]

That's strange. You have negative crankcase pressure. How are each of your breather tubes routed? The smaller one should connect to the the intake pipe and the larger one should pass through a PCV valve then to the front of the intake manifold. Did you happen to notice missing or broken baffles while the valve cover was off? You seem to have excessive vacuum to the crankcase. It's probably consuming a bit of oil too which could cause misfires in severe cases.

 

[MotherShip]

That's strange. You have negative crankcase pressure. How are each of your breather tubes routed? The smaller one should connect to the the intake pipe and the larger one should pass through a PCV valve then to the front of the intake manifold. Did you happen to notice missing or broken baffles while the valve cover was off? You seem to have excessive vacuum to the crankcase. It's probably consuming a bit of oil too which could cause misfires in severe cases.

THANK YOU
While I was replacing the gasket my father replaced a cracked hose that had the PCV valve and routed it directly to the intake.
I didn't really think of it until you mentioned it was a valve. Lucky he didn't throw it away and I got it back on and now it's running normal again