1989 Oldsmobile Ciera Stalls and Check Engine Light is on

The Car recently started acting up. It's cold here around 20 deg and when I start the car up it chugs as if it's a diesel engine on a cold morning. It does this for about 5 min then begins to run normally. The check engine light is already on at this point and the car has trouble idling at stops to a point where it will actually stall. One in motion it's usually ok, but there are times when it feels like the car is lacking motivation to move forward. The check engine comes on and off. And when it's off the car runs just fine. What might be the problem or where should I start looking.