2008 Mazda 3 i misfire p0300

Ok so I’m having a p0300 code on my 2008 Mazda 3
-after market exhaust, air intake, and tuning
-rough idle and cold start
-replaced cover head gasket, spark plugs, 1st fuel injector, MAF Sensor
-At first it was a misfire for cylinder 2 then while working on the injectors (I swapped them around) it switched to the first cylinder, I then replaced just the one injector and that led to the p0300 code
What should I do cause now I’m lost?

 

Could be bad coil packs and properly gaoped spark plugs. Gotta get oem coil packs as Amazon or aftermarket coil packs are known to be shit and not fix the situation. Ngk plugs are a win.

 

Plug gaps 0.26-0.28. new recommended ngk plugs so you can rule plugs out. Stock coils. Verify which cylinder is misfire. Swap coils, see if misfire moves. That's the easiest. When you removed injector, did you replace all the injector seals? No? Then to eliminate that unknown gotta do them. Search site for cheapest rockauto kit ($45?) After all that, comes harder part. Air leak elimination. Follow intake air path pre/post turbo look for air leakages.