First double check that all the plugwires are pused all the way on the plugs, and that they are all going to the right cylinder. Not questioning your abilities, but its best to start with the easy stuff. Also check all your wiring to make sure it is not rubbed through anywhere.
Brake Cleaner - It will change the idle, might cause it to rev up instead of dieing down. Also spray around the intake to check for a leak there. Avoide plugwires, coils, and exhaust manifolds- we dont want a fire.
P0300 - More then likely if it was an injector(or coil) this code would have a buddy code- saying what clylinder(s) have the misfire
Low fuel pressure can cause this code - hard to test without a gage.
A crank position sensor can cause this issue when it starts going bad - common problem on these engins
Also an ignition control module(the thing the coil packs sit on) can cause this code.
