Hello I have a 2006 Volvo s40 2.4 non turbo. I did a head job and new timing parts. I started it after I finished and it had a ruff idle bad miss. So I checked my lines replaced the weird on with multiple heads seemed better but still bad idle. I then replaced the fuel pressure sensor and test the fuel pressure had 55 pounds Seemed better but still bad idle. I replaced the plugs and coils sounded much better barley a miss but sounds like 2 maybe just off of ear. I don’t know how long it sat for so maybe bad gas? I’ve read that a bad O2 sensor could cause it I did have to remove the exhaust manifold so I took it back off to see if that was it no difference