One question.

What brand and number plug did you take out, and what brand and number plug did you put in? Also what brand and type plug wires were used? Sounds like a problem I had on my 84 500 SEL.
I had the wrong plugs, and the wrong coil to dist wire, (it was a resistor wire and should be a solid core wire).

__________________
84 500 SEL (307,xxx miles)