Generally if the fuel pressure regulator was going faulty the diaphragm would leak and you would notice petrol exiting up through the small hose to your air filter. You would notice a fuel smell.

Have you changed the fuel filters and accumulator? Have you had the fuel system pressure tested? Fuel pump relay? (intermittent fault)

How are your lifters?None noisy?

Just adjacent your IACV on the manifold there is an grounding junction point. If you have corrosion on this point or the bolt holding the wiring down is corroded this can have an impact on the electrical parts of the injection system.

If you disconnect the wires from the EHA and IACV this will take the electrical portion of the injection out of the equation. The car will run on pure fuel injection with no electrical adjustments and the sensors become ineffectual. If you do this does the engine still misfire? At idle the engine should rev up to around 1100 rpm. - No iacv controlling the idle.

The engine must have no misfire otherwise the sensors will give faulty information to the ECU. This will inturn make the ECU send incorrect information to the ignition and fuel controllers. Your plugs, leads dissy, rotor and engine condition must be good.

Your engine is very clean. Generally if the valve stem seals have gone then there should be some crud and dirtiness around the valve and rocker lifter area.