You also mentioned it came back in the morning.
Could it be the air temp sensor? Maybe this is giving readings which allow the car to function well once warmed up, but in the morning when the air is colder, more dense, the fuel / air ratio is off?
I think it should read about 2300 ohms in Todays temperatures. If yours was reading lower than this (falsely hotter air temp reading), it might cause the
to mess the mixture up especially when the air is really colder.