Replaced alternator... new problem presents itself

[Arpegius]

I completed installing a used alternator into my '89 325i. It starts fine and idles perfectly. The problem is, when I give it some gas and let off the pedal, the revs drop to way below normal idle speed and it sounds like its going to die. It quickly boosts back up to normal idle speeds and stays that way until I of course open the throttle a bit. I hadn't noticed anything like this until just now. I could be paranoid, but a mechanic said it could be a vacuum leak. Any suggestions?

[jlevie]

Vacuum leak and/or sticky ICV.

[Arpegius]

Very strange. So I drove it around a little bit more, took it to les schwab to have my front alignment adjusted. The mechanic test drove it. When I got back in my car to leave, the problem was gone. I drove home turned it off, waited, turned it back on, and drove around a little bit more. The strange chugging idle seems to have miraculously fixed itself. I will test it again tomorrow to see how it runs. I hope this isn't just a fluke.

[a_thomasmr23]

if you had the battery out for about 5-10mins the computer had to relearn its settings which just takes some driving around

[Arpegius]

That makes sense now that you mention it. Thanks.