07 Fit with 165k miles on it. This car has been an anomaly since I got it. I’ve replaced coil packs with OEM, spark plugs with NGK, new alternator, new battery, valve adjustment was done, upstream O2 sensor replaced. When valve adjustment was done I was told the engine is impeccably clean inside. After replacing the alternator the car felt like new it was completely smooth in all aspects of driving then about 2 weeks later the rough idling resumed. After that I scoured the forums more and everybody was like valve adjustment for this issue and ended up with the same story. 2 weeks later now it’s back to idling rough and for the first time since I changed the battery about 6 months ago it had a hard time cranking. I don’t know what else it could be. Idling is so bad the car feels like a rocking chair however once the car gets driving and gets over 1k RPM there’s no issues.

 

Got any video with the hood open of the engine running during the rough idle? My random thoughts are that perhaps you have a damaged wire to one of the coil packs (rodents or something like that) or perhaps a wrecked engine mount that's letting the engine move around a lot. Also probably worth disconnecting the rubber intake hose and looking at the throttle body to see if it's caked in carbon or anything, which could contribute to rough idle.