I have the same car and my smog pump went bad at 77,000 miles. The symptom is a shriek on cold starts that may last 30 to 45 seconds. There are a number of good posts on this board -- just search under "smog pump".
The prior owner probably disconnected it to stop the shriek. While the car will appear to run fine without it, I understand that in time the catalytic convertor can be damaged -- and as the convertor is a couple of thousand $$, I am going ahead and fixing mine.
A new pump is $600, but a rebuilt pump can be obtained for under $300 from BenzBin (http://www.benzbin.com -- ask for Paul) -- you will need to return your old pump for credit (you are charged $500 and get $200 back when the old pump is returned). I understand that the labor is minimal -- just disconnect the belt, unplug the hose to the pump and there are two bolts to remove and install it.