erratic idle, engine stumbling, etc in a 89 saab 900s

[pepper]

So i bought my dream car, an 89 900 about a week ago. I bought it because it started and ran well, and regardless of some problems (oil leak and no power steering) I wanted to turn this into the car I learn how to fix. Well lucky me cuz now I get the chance BIG TIME (just kidding, Im pissed) For the past 2 days the car very suddenly started idling very erratically, seeming like it might die at stop signs, then alternately lurching like the brakes cant hold it back. When driving from a braked position the car sounds like a golf cart, sputtering and hard to speed up quick. As for the rpms, it idles a bit over 1000, and sometimes the needle doesnt work, but is never much over 3000, even when going up to 50, from about 35 mph up it runs a little loud, but no more lurching or stumbling. Since this problem the check engine light has never come on, but the shift up light comes on intermittantly. Ok, so from this I'm sure you can see I am no car expert. I understand I should first check the vacuum hoses, then what steps and what order do I take them?
Ummm the car's an automatic trans, has a pretty substantial oil leak... One thing that I was wondering, is there an issue that sounds like this that the guy that sold me the car couldve concealed until I drove the car ~75 miles, only to have it show up again later, or is it a coincidence that it drove. great and broke a few days later? Ie he quick fixed it? I thought if that was the case it might be a diagnostic clue?!! Im trying to be a gumshoe here, any info would be ever so greatly appreciated!!!