Kia's Rough Idle
This bulletin applies to 2014-2015 Kia Cadenza vehicles equipped with a 3.3L GDI (gasoline direct injection) engine. When addressing a customer complaint of a rough idle, which occurs only at the first start of the day and lasts for about 30-45 seconds, check for the possibility of poor injector performance in a particular cylinder. This concern may feel like a misfire. However, it is not an emission or catalyst-damaging misfire, and it does not typically trigger any DTCs.
To diagnose this concern, go to KDS > Data Analysis > Engine and monitor for current misfire counts on all six cylinders during the first cold start in the morning to assist in determining which cylinder is responsible for the rough idle conditions. Replace only the injector for the affected cylinder. To verify the repair, recheck again after an overnight cold soak to make sure that the rough idle is no longer present.