Chevrolet: rough idle, chevrolet camaro, litre engine

Question
1998 Chevrolet Camaro, 3.8 Litre engine, standard trans. The code P300 keeps appearing as I scan the codes, and this is after a code for a faulty Os sensor was found and replaced. I also found that I had a hard start condition, cranked okay but took many revolutions before firing. Found no fuel pressure so I replaced the fuel pressure valve in the fuel rail. This fixed the hard start problem, but I have a very rough idle and the only code thats ets now is the one I emntioned above, P300, random missfire. Also have installed brand new spark plugs and wires. This engine starts terrific since I changed the pressure regulator valve, but still has a very rough idle. Very good power and it smooths out around 2,000 RPM. There is also a strong odor of fuel from the exhaust, just like it is running very rich. Any help would be appreciated as I am at about wits end.

Answer
Did you check the fuel pressure to see if was within specs after replacing the regulator. It is very rare to have a bad regulator on this engine but very common to have a fuel injector stuck open, which will cause a rough idle, a rich mixture, and will smooth out at higher RPM. If the scanner will show history misfires, the cylinder with the most misfires is probably the one that is leaking. If your scanner wont show it then you will have to do an injector drop test.