RPM surge when in park & in motion

I have a 97 delta 88 LS that starts fine, After running for a while it starts to rev up and down on its own its still in park it gos on for a while almost stalling and then regaining power then finally stalls. This happens while driving to, It stalls out but there is no problem restarting. Im looking for a starting point to solve this issue only thing i have changed is the fuel filter fixed a vacuum leak and problem is still there.

Start by cleaning the throttle body also remove they EGR and clean it, although they have been known to go bad and cause the same condition, there are other common causes for this condition, but these are the cheap easy starting points.