1998 Chevy Lumina THROTTLE BODY, THROTTLE POSITION SENSOR

When you changed the EGR valve, did you check to make sure the port on the intake where it attaches was unclogged? Often, the problem is not the EGR valve itself but the inside of the intake manifold, which gets coated with gummy stuff and even plugged up with carbon where the hot gases from the EGR hits it.

For the throttle position sensor, if it's not outputting a signal, something's wrong in the wiring or sensor.