the idle. If the EGR is leaking air then it needs to be fixed or replaced. If the diaphram holds vacuum then that portion of the EGR is OK. If ther EGR is leaking at its base gasket then that leak would let air into the plenum and effect idle. I suggest you also place a vacuum gage on the engine downstream of the throttle body to checks for leaks. I use the port on the passanger side of the balance tube to connect the vacuum gage. My 92 NA reads a very steady needle at 20" Hg at idle and steady needle at 21 " Hg at 2000 rpm.
Low readings with vibrating needle would indicate leaks and other issues. Here is a link to aid in vacuum readings