Help! Erratic Idle on a '90 300SE

[cam69ss]

Hi,
Just changed air filter, removed and cleaned the air cleaner housing. It used to idle at 700-750 rpm or so but since the new filter it is at 1100-1200 and it will idle erratically, sometimes jumping from 1100-2000 and back again in a second. I checked the vacuum lines and I did not see any off or cracked. It has been very cold 0-15 deg F but I didn't have trouble before when it was cold out. Anybody know what could be causing this? What I should look at?

Thanks,
Dan