I'm trying to figure out if anyone else is having the same problem as I am. My 3800 is misfiring on the 2 and 5 coil. I replaced it and still the same. I'm thinking CMU? This morning the car started and slowly idled up all the way to 4000 rpm. I had to jump in skivies and go shut it off. Then it started fine and idle correctly. Sometimes the car idles bad due to the misfire and stalls out. Any ideas? I had a 3800 in a lesabre that went 254,000 miles and still ran great. I never did anything to that car. I'm at 136,000 with this one and am puzzled.

Test all your coils and plug wires. Inspect the plugs and post pistures of them if you can.

I'd seen the creeping/high idle on my 1994 when the throttle position sensor went bad. Check/disconnect your TPS and see if you still get the weird idle. You might be chasing two separate problems (idle weirdness and misfire) or the PCM getting bad data from the TPS could be causing issues.