1989 Skylark Problem: Gas Guzzler

I just aquired a 1989 Skylark 3.3L FI sedan. It runs rough at idle, but has plenty of pep on accelleration. Problem is it's getting about 9 mpg. There were several recalls in the early 90's for "miss, hesitation or roughness" but Buick can tell me nothing about this. Does anyone have any idea why this engine runs so rough at idle and consumes so much gas? Is it the Mass Air Flow sensor, or the Idle Air Control Motor, or the Oxygen Sensor?
Any help would be greatly appreciated.
Thanks
Sean Myth
seanmyth682@lycos.com