FormulaTA327

My cousin has a 01 z28 and it's throwing code P0300 and P0174, had good spark plugs in already, then put a different stock MAF on it and nothing changed, then swapped o2 sensors from left to right, it showed different on the hp tuners when we did that, we then put a new O2 in replace of the expected bad one, nothing changed, what else could it be

cucui

iTrader: (2)

have you checked for a vacuum leak or check for a dirty fuel filter and proper fuel pressure

FormulaTA327

Fuel pressure is good, didn't check for vaccum leak

xenergyx

iTrader: (3)

Excuse my ignorance but how do you check for a vaccum leak when the car is running cant hear **** lol or am I just missing something ?

FormulaTA327

Spray carb cleaner in the suspected area and the idle should change

LS6427

iTrader: (2)

You probably checked this, but a lot of times after a plug change some of the spark plug wires might be touching the metal exhaust manifold piping. That causes multiple misfires codes to pop up.

Really bad tank of gas.....
Bend valves.....( did he hit e rev limiter lately.)
Clogged fuel injectors......
Leaky fuel injectors.....unlikely it's more than one though

Definitely hit the entire border around the intake to check all 8 intake gaskets, those leak a lot.

.

FormulaTA327

Could be bad gas since he hasn't drove it in over a month, he just mentioned that he hit some ice last winter and it started acting up after that, could have messed up the wires on the o2 sensor