Changed the battery now the idle is surging?

I just changed the battery in my girlfriends car. When we started it the idle now drops to 500 then shoots up to 1000 and may even stall. This is only when it idles, while driving it is fine.

Any ideas what this could be? I did remove the upper half of the air cleaner but I replaced the connector on the sensor.

If it shoot ups after idling so low, I heard thats a way of the card to prevent itself from dying out. Not sure if its true or not.

Also, need some more info on the year and model too.

1991 3.1l auto

This is really just beyond me what changeing the battery could have done. It isn't the correct barrery it's a GM side terminal battery from a 91 Camaro 5.0l which is a little bit smaller but the specs on it are the same.

Dirve the car a little and see if it stop surging. The computer has to re-learn sensor signals (unhooking the battery on 94-older GM cars clears the computer). The surging idle is normal during this re-learning period. It takes a certain number of events for the computer to make it's adjustments, so just drive it over varying types of driving (stop and go, a little x-way cruise, idle for a few minutes, etc....) to finish the relearn process. If doing this doesn't help, re-post and we'll get into what may be wrong.

It actually had been driven a bit like that and didn't show any improvement.

I got the correct battery for it which is a little bigger then went through the idle learn process. It got alot better after that then with a little driveing is now gone. Thank you very much for the help. I think I'm going to run back to my carburetors now :)

Glad to hear you switched to the proper battery and everything works :)

just in case the problem persists:

make sure the cables are good, sometimes when they get old they do not connect very well to the battery, and the computer could be getting burts of voltage. also, check your grounds for good connection.

Maybe if you actually knew how to work on something other than your beater Camaro you'd have figured this out from the start. :)

Don't worry, I'm not stalking you Pyro. I've been here a little while...