Love this engine but having an issue
So I’ve had this car for a few years never had any real issues besides the notorious bank two sensor two o2 sensor code, which doesn’t really affect anything besides cat efficiency. However, one night after washing my engine bay the car started sputtering and misfiring. I wrote this off as water in the spark plug wells, and I let it idle and dry out and then it was OK. Fast forward a few weeks the problem returns, but I know there’s not water in there. I checked everything, however I did notice that I had a pretty nasty valve cover leak which I thought maybe that’s probably why the spark plugs are not doing their job because they’re covered in oil so recently I replaced the valve cover gaskets and clean the spark plugs and all the ignition coils and wires Make sure there’s no problems connect all the connectors properly and even when I hooked up a scan tool before I did the repair there was no misfire data for anything. I did have a mass airflow sensor intake air temp code, which I then fixed but from now there’s no codes besides the O2 sensor code so I’m assuming maybe there’s possibly a problem with my fuel system and I need to clean it out. as far as I’ve owned it I’ve never done anything with the fuel system. I don’t think the previous owner did as well. The car has about 263,000 miles I’ve owned it since 220,000. Now for modifications, I’ve done to the car. I’ve only done headers to the engine, and the car is manual swapped, which I know on its own brings different performance problems if you don’t tune the car properly which it did before with a little bit of lag, but it didn’t sputter now I do plan to get the car tuned, but I don’t believe this is the root of the problem because it’s not all the time. the car will misfire under load like when I let out the clutch and give it gas to get up to speed if I give enough throttle. sometimes it’s not as bad sometimes it is and it flutters. if I try to rev match it revs Slowly when I idle it only does it when it’s hot or there’s a load on the engine or the AC is on so if you guys could help me out if anybody else has had this problem, it’s bugging me because this car’s never done this and I love this car too much to have this problem