I've been chasing a misfire at idle in my '93 Eldo 4.9 for some time. It is progressively worse as the engine reaches higher operating temperatures such as in traffic in warm weather. It is also progressively more noticeable as more load is put on the engine such as putting it in gear or turning on the A/C. Plugs, wires, cap rotor, coil, injectors, FPR, pump pressure, etc., all check out OK. Those parts have all been replaced or tested according to the FSM. No codes. No discernible vacuum leaks.
Can an ignition module begin to fail slowly producing these kind of symptoms prior to complete failure? I know they can have intermittent failure due to heat and produce a no start condition. I'm out of ideas and would rather not wait for a precipitous failure to fix this. Any guidance would be most appreciated.