2001 windstar too lean system

had to put a heater core in my 2001 windstar 3.8 today,it was running great before but after it seems to had a little up and down to the idle,too lean seniors bank one and two same on ,i cleaned with my code scanner,and put 92 oct with gas treatment it,helped but bank one senior still came on and it still has a fant up and down idle,keep thinking its to do with installing heater core,again it was running fine before i installed it