Help, jerking and misfires

I have a 2.5L RS stock except for intake, full exhuast. Yesterday I was going about 50 in 3rd gear, ~4000rpm I think, and as I brought it down it started sputtering and took it home and idle was rough, real rough, shakes the whole car and you can hear detonation in the exhaust, I don't have titanium so trying to fix asap as is my dd. I've replaced the fuel filter, knock sensor (don't remember brand), replaced throttle body and cleaned IACV a while, but cleaned out IACV again yesterday. Replaced plugs and valve gasket set all within 10k ago. Somehow, I checked, there was little to no oil, filled it up, my bad for not checking sooner, but doesn't seem to be the culprit. Also small traces of oil in plugs already? 1 or 4 cylinders I believe. Before I replaced them I'm sure it ran with oil on plugs for 30k and was fine, so don't believe that it would retard the timing to what it is. Haven't checked wires or coil pack yet, recently replaced o2 sensor, BUT wasn't new. Also recently filled up and dad suggested water in my gas, added a treatment and trying to burn up the gas to disprove or prove that theory. I have two p0031 codes, one of them is old I think, other is new, either way....Also have p0507 and p1507 which looking at descriptions seem to all be related in the sense that you fix the p0031 and the rest go away (correct me if I'm wrong). Any help much appreciated, thanks.

Codes:
P0031 HO2S Heater Control Circuit Low (Bank 1 Sensor 1)
P0507 Idle Control System RPM Higher than Expected
P1507 Idle Control System Malfunction (Fail-safe)
(pretty sure the last two were from when my IACV was dirty...idled about 950 rpm for a while til i fixed it, purred til last night)