which idle screw? if you mean the one on the AFM then that was a big mistake. but yo have ems so i guess not.
if you mean the one on the throttle body, you need to also adjust the TPS to ensure it's sending the right signals at throttle opening %'s and returns to idle mode etc.
in winter i wouldn't suggest the colder plugs as well as smaller gap, this can case misfire from not enough or hot enough spark.
check that it's firing@10 deg BTDC
what boost are you running?