Ford Escort Wagon 97

82k miles. Automatic. The car has a problem when at a stop. When in 'drive' and at a stop, the idle bounces from 600 to 900 rpm. It is chugging. Sometimes goes even so far as to stall. Putting the car in neutral helps alot. Usually idles fine at 900 rpm although if left idling log enough, it has idle trouble as well and will stall. This has been getting worse over the last week and now the check engine light has come on.

I got an oil change today, so I had them do the air and fuel filter as well. I also put in a fuel additive. While I'm waiting to see if this helps, is there anything else that comes to mind for this problem?

Thanks!