Hi, when I throttle up my engine and hold the throttle steady at say 2,000 rpms the engine revs up and down at steady throttle about 500 rmp up and down . it does this at any throttle level just up and down revving.
Any ideas??

Thanks!!

 

I'd probably start with some basic diagnostics: check for vacuum leaks, pull codes (even if the CEL isn't on), check fuel pressure.