1989 Buick Electra check engine light code 42 (ignition)displayed yesterday when the engine stumbled and lost some power while driving. I figured the coil pack would have leaked the green stuff and warned me that it was about to fail. Changed old Magnavox ignition coil to the upgraded 3 coil/module from later model 3800 vehicles that I had plans to change anyway. The car idled a little rough, but had no problem accelerating. Not satisfied with rough idle, I change yet again to another old style Magnavox coil that I knew was good and the smooth idle has returned. The upgraded coil and module tested all good, so curious if anyone has experienced a rough idle after upgrading the old Magnavox coil on the 3800 engine?

Did you apply thermal paste between the ICM and the mounting plate/heat sink? This is an important step and should not be overlooked. Your ICM could be overheating if you didn't do this, which would easily cause your misfires and lack of power.

As for rough idle, I've also done the Delco swap on my '91 LeSabre 3800, and I have noticed that it does seem to idle lower. It'* not quite as it was with the Magnavox ignition. However, the car otherwise runs great, throttle response seems better, and MPG seems to have gone up slightly, so I can live happily with a lower idle.

*Quite as smooth. Whoops.