97 escort 2.0 rough idle

Hey I recently replaced the Emmissions purge flow sensor cause my check engine light was on, I was hoping that would take care of my rough idle and varying rpms but it hasn't. Basicly when I'm at a stop or in park, sometimes the rpms start to dip down and it sounds like im reving the engine when I'm not. Somtimes it happens really bad, sometimes minor, sometimes not at all. Any ideas on what it could be? It has been doing it for a while, I'd appreciate any help, thanks.

Check for a vacuum leak and then check and clean both the throttle body and the idle air control motor. This should cure the idle problem.