Is there a certain procedure to check the MAF? Also, how would i go about performing a vacuum leak test? aside from visually inspecting. Thank you

Hello, I have a 2004 Volvo XC90 T6. with 100k miles. The CEL is blinking. Checked codes and shows misfire in 1,4,6. I changed, coil packs and same. I changed the spark plugs, same. Changed injectors and same problem persist. If I let it idle, it sounds really rough. I dont know where else to check ...