RPMs will fluctuate slightly and cause the lights to dim along with it?

My problems started with a lean code that went away once the MAF was replaced. Also replaced alternator simultaneously. Since then, I've been having this issue with a sort of engine surge where the RPM's will fluctuate slightly and cause the lights to dim along with it. This happens intermittently and occurs when the car is in park or while in drive at a stop. Recently replaced battery, alternator twice (issue persisted with both rebuilt alternators), serpentine belt, ground wiring, MAF sensor, ignition coils, spark plugs, and PCM. There was also oil found in one of the coils, but the surging problem still persists with new ones installed. The valve cover was replaced. No vacuum leaks were found and the charging system checked out fine. Have been chasing this issue for over a year with no luck.