Hello I’ve had this issue with my 2006 s40 2.4 I did a head job new timing head was milled new gaskets everywhere. I started it and it had a super ruff idle to where it would stall replaced the vacuum hose with multiple ends in it seemed better. I then replaced the fuel pressure sensor and test the fuel pressure and it read 54 pounds. Replaced the coil packs and spark plugs now just has a slight miss it sounds like cylinder 1-2 have it. The only code I’ve gotten is P0300 random multi miss it doesn’t give me a CEL just when I put the scanner on it. I bought this car for a flip so I don’t know probably next move is to drop the tank and remove all the old gas. Since I don’t know how long it sat didn’t seem like it was long from the paint.