So I have an 04 6spd.

I've had a misfire problem haunting me for the last few months. Here are the symptoms:

Rough idle, kinda jumps up and down from 300-800 or so. Never above 1000.
-Its never really stalled at idle too often, but the other day it did stall while I was at a red light.
-When giving the car moderate gas, somewhere in the 4500-6000 range, the car will stumble, then when I let off the gas the exhaust will backfire a little pop.
-Revving it constantly will yield the misfire.
-Used to, if I'd go high speeds (80+), full throttle, it would continuously misfire but from what I could tell no affect in performance or stumbling. Just flashing CEL.
-Recently, starting the car takes about 3-4seconds, hot or cold.


The only code showing is a P0300. Here is a list of everything I've done so far:

New coils
New wires
New spark plugs
Seafoamed twice (with 2 cycle oil to boot)
Cleaned MAF sensor
Cleaned ESS & reset
Cleaned cold air intake & replaced filter with new one
New rear o2 sensor, front still hasn't been changed
It has a Black Halo Racing Midpipe, so no problems with buildup in a cat.
Numerous over the counter fuel injector cleaners, but never professionally cleaned


The only other things I can think of is:
Vacuum leak
Compression (going to get it tested next week, quoted $200)
Fuel injectors
Fuel pump

Anyone have any suggestions before I get the test as to what this sounds like?

Thank you.

 

I was going to suggest your "other things I can think of" list.
Check for leaks
Check your fuel filter and pump
Double check your wire connections, plug and coils installation