Coils Going Bad
Do you have AC Delco Plugs?
When I purchased this 93 SSEi (118K Miles) for my son we did a total tune up including new wires and Bosch Platinumí*. It always had a little roughness to it. Then the coils started going out, only 1 cylinder per coil, but two different coils. Then later, the third coil went bad. After changing coils again, I chatted with the local GM mechanic. He was pretty arrogant, but right.......as he said the 3.8L GMs do not like the higher resistive Platinumí* and will not run as good (he actually called them JUNK, but good for imports) . We changed them out for $1.25 AC Delco plugs....then runs like a dream. No roughness at all....smooooooth, and knock on wood, no more coil issues with a 140K now. SSEi getting 25 mpg @70 on the road.