I bought an 04 CTS auto with the 3.6 about a week ago. One owner, full service records at the same Cadillac service dealer from the day they bought the car to the day they sold it to me. Fully maintained and have preferred customer stickers everywhere from being serviced there for so long lol. Car runs great and I love it.

The issue im having is a 1-200 rpm idle rpms fluctuation consistently when its doing it, but it doesn't always do it at idle, also when cruising round 1700-2000 rpm you can see and just barely feel it fluctuating. There was no check engine light but I hooked my scanner up and found a hidden MAF code for something like low input. Cleared the code. I have put in fuel system cleaner as well as injector cleaner and also have ran some higher grade fuel. Havent seen the code pop back up yet, but starting yesterday if you get on it from a stop the check engine light would start flashing then turn off. Finally it did it again doing the same thing and it stayed on and read a P0301 cylinder 1 misfire still no maf code. Today I replaced all the plugs with OE style plugs, checked all connections as well as cleaned the MAF sensor and replaced the air filter. Car runs a bit better now but still the same idle fluctuation. Im going to drive it some more tomorrow and check for codes again.

Any ideas/sugguestions? Im going to run regular grade for now on and add in fuel injector cleaner. Only thing I can think of is the #1 cylinder Coil. I have a new one purchased and waiting to be put in but I can get one online for $28 instead of the $71 I paid for this so Im going to take it back and order the oe online if this may be the problem. I know my grandparents have a 07ish model F150 with the same style coils and was having a miss but couldn't ever get the check engine light to stay on to get a code but it ended up being the coil.

Thanks for any help.