Looking For Some Advice With All These Misfire Codes!

[Valero1990]

Hello, Im a new member on here but have been reading posts and learning about this problem and getting some ideas. I had a bad o2 for a while (Bank2 sensor1) I finally changed it and it was a little tough unplugging the connector with all the hoses in your way. I did it with not that much of a problem and over a few years i have changed all the other o2's also. Car is a 2001 gs300. Now what is strange is after i changed the O2 i reset the ecu and started it up shut it off. I used it soon after and it started running a bit strange like never before. It almost felt like water in the gas. It was bogging and i couldnt understand what did this have to do with installing the O2. There is no cel on yet either. Whwn in park if i rev it up it sounded like it was misfiring. The next day i started it up again and cel was flashing and vsc off light on also. I scanned it and P0300,0304,0305,0306. It obviosly was a misfire. Car has 160k and has original plugs & wires. I figured it may have a problem with that all of a sudden, so i bought plugs & wires. Bought ngk iridium if i spell it correct which sound like the good ones. I did reset the ecu again and the cel has not come back on yet but still does not run good. I started to prepare to change the plugs which i know is not a fast job. I pulled off the engine cover so i could see whats in store for me.I was looking around and did notice the the pcv hose running right over the O2 connector was cracked where it goes onto the pcv. It was very dry & brittle and i may have bumped it and didnt see it until the cover came off. I put a new hose on with a 5/8 piece i had in the garage and i did order one from the dealer cause i do like to keep my car original as possible with the engine! I went for another local ride and it did feel like it was a little better. When i step on it it feels like it wants to clean itself out and it runs good while the pedal is to the floor. Its just weird how this happened right after i changed the O2 and cant understand how. If anyone has any idea or advice on what i should try first that may cure this problem. Im sure the plugs should be done but really cant see how they would instantly go bad when changing the O2. I would appreciate Any advive! Thank You - Paul