Have you checked for vacuum leaks at the washers under the injector holders or the washers mounted on the injectors(2 per injector)or at the brake vacuum boost check valve. Use either brakekleen and squirt it or a small UNLIT propane torch opened just a bit and pointed at the potential source of the leak, or a long plastic tube...........one end in your ear and the other at the source of possible leak. With the tube method you need to distinguish between plain old engine noise and a sucking or whistling sound which is a sign of a vacuum leak.

Alternatively, it could be running lean so the idle is hunting. Perhaps that occurs on an uphill because the in tank fuel filter is gummed up. I cant comment on EGR. I have a 72 164 without EGR although I suppose its a possible source for the problem