Goodman GMES96 air switch sputter

[chillerelvis]

Installed furnace 8/21 and has been having problems since.  First the condensate line plugged and caused water to fill inducer motor.  Now flame sputters erratically due to air switch.  Read -1,70 on switch and when blower comes on it bounces from -1.7" to -1.3".  It's in Montana where negative temps are often.  Any thoughts