m40 518 question

[jclbmw]

being new to owning 93 518 with the m40 engine, i was hoping someone could answer a question or two. it runs great, about 115k. it seems to have alot of tapping noise in the engine as if valve adjustment was off or it had a bad lifter. not being familiar with this engine, is the m40 just an inherantly noisy engine? does it have traditional rocker arms with eccentrics like the m20, or does it have a setup more similar to a m50 engine? last but not least, when you get up to around 4-4.5k rpm, it starts to run poor, sounds like its missing. perhaps an ignition issue. the previous owner mentioned something about the rev limiter acting up causing the issue. does it have a limiter and would it cause this particular issue. any help would be greatly appriciated. thanks.