Check for loose or damaged wires to your EGR system… EGR may need replaced or cleaned… However the oil situation is of larger concern…..
Check your oil level and oil condition (no coolant, weird colors, etc…)… If your oil condition and level is fine then you probably have bad bearings (shown by loss of oil pressure)… When bearings start going bad, the oil pressure gets low enough to trigger the oil pressure light… this stays on until the oil pump can pump a greater volume of oil through the system (Higher RPM’s)…
Also, oil pressure may not be low enough to initially trip the Oil Light when the engine is cold because the oil is still cold and not as viscous. When it warms up and gets less viscous and while at idle, the pressure drops and the light kicks… Classic symptom…
Also, it may be a good idea to check the oil pressure mechanically if the oil condition and level are good and the light is still running (before you decide to rebuild or replace enging) The problem could be electrical or the sending unit, but the chances of that are much less… also these engines were known to sludge, so a good inspection of the oil pickup screen may be in order as well..
Good luck.
Karl