Posting for a good buddy... really I am.
He got his son a 2001 XJ for his first vehicle. Ran great until he washed the engine and it started running rough. Starts up fine, shakes at idle and slow speed, 45mph and up is runs better.
Been a long time since then and it still doesn't run right so it's not just components getting wet.
He has replaced coils packs, plugs, wire, injectors, and sensors. Says he has cleaned every connector as well. He says he can disconnect the injector wires on the first 3 cylinders one at a time and no change in the way it runs, if he pulls any of the rear 3 cylinder injector plugs the engine runs worse so he thinks it's something in the front 3 cylinders. Says when running you can smell raw fuel and in the shop it's bad enough to burn your eyes.

The XJ does have 220K miles.

Ideas?

He is thinking something in the valvetrain is stuck/broke or head gasket.
I advised him on the 0331 head issue but would like to gather more suggestions before he goes through that.