Hello it's been a long time since I used the forums 5-6 yrs probably. I've been having trouble with my 2009 fully bolted and tuned lnf. It's been tuned on hptuners @ 24lbs conservative about 6 years ago. James rakes (rptuned), I know before all the hate this guy gets, I filled up on sunoco premium gas 93 Oct. (like always) That morning on the ride to work, I get on it alittle in boost its fine then all of a sudden around 2-3k rpms it starts to stumble miss fire and hesitate like mad. It does fine revving after 3k rpms. Pop pop around 5k and decel. Backfire. I am catless for a while I notice alittle more black smoke Than usual during idle when I got home idle is rough. Not super bad but rougher than normal. I been on the bad gas band wagon thinking thats all it may be. So I drained some gas and changed the plugs. It ran great with the new plugs (acdelco stock). Until the next morning, rough idle boggin and bucking in first and second gear. Bad enough I just wanted to go back home. Added some seafoam to treat the intake valves. And Lucas fuel cleaner same results. Cleared the codes same ones come back miss fire cylinder 1 2 34,. I haven't changed the fuel filter. And this car was never beat on I'm the second owner. Tune was great for 6 yrs. No issues. Car has around 87k miles any help my next move would be greatly appreciated.
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​​​​​​All your O2 sensor codes code are probably disabled since you are Catless maybe start looking at O2 sensors.... I don't really know that they would cause random misfires on all cylinders, but who knows.

 

Bad primary o2 sensor can cause misfires on all cylinders.

Hopefully the tune hasn't shut off codes so they don't set.

Seafoam doesn't do dick to the intake runners that get coked up, I'd pull your plugs and visually inspect them. Also get a log of what is happening, that can help figuring out if another sensor is starting to fail or reading incorrectly (maf vs ve, tmap vs map, etc. etc.)