Before I started to work on it, the car was parked for several years, except for now and then to run the engine.

Plugs are new. Cap and rotor looked almost new. Wires look good. PCV was removed and checked (I did buy a new one, but it does not seem to be a perfect fit into the grommet. The original one has a barb at the end, the new one was smooth). Vacuum lines look good. Valve clearance was adjusted per spec. Timing belt was inspected and retensioned at the same time.

Since the ecu is pre-OBD2, I assume there is no DTC for O2 sensor slow response, which could account for the peaks in the emissions.

What bothers me is that the peaks in the emission graphs coincide with acceleration, and so does the unusually loud and rough sounding engine. Sounds a bit like the old GM "Iron Duke" engine did on open throttle...