2012 Chevrolet Impala- CEL off and on

2012 Chevrolet Impala LS check engine light goes off and on. Register reading is the fuel flex sensor. It was replaced. came back bad again. replaced. same result. Stays on solid. Changed the PCM - light went off, came back on. accelerate and it goes off, idles it stays on. This is a flex fuel sensor vehicle. Anyone had this same issue? Vehicle light no

Some have had problems when switching to or from E85. the vehicle needed to be recalibrated with a dealer scan tool to fix the problem.