after dead battery, stupid idle HELP
 

I was a moron and forgot about the parking lights today and the lights drained the battery. So I had AAA come out and give me a jump, and all was well. But once I set off and only moments after the car had started there was a really really loud and bad screeching noise coming from the engine bay which was not there before the jump start. I looked at the engine after I had driven for a few blocks and the accessory drive belts(or something atatched to them) seemed to be making the noise.

Now the squeal has quieted down but the idle has gone all stupid, when off throttle going down to 300rpm and making the car shake and shudder as if it was about to stall.

Do I need to reset the idle somehow? I have had this happen before and the car was normal after being re-started, but now it isn't. Could I need a new battery? Alternator?

I don't know what to do, but this is worrying.

check your alternator tensioner.

Well I tightened it, and nothing seems to have changed. After I rev the engine the idle drops between 300 and 500 and pulsates a bit. After a while it goes back up to about 8 or 900 rpm.

Any ideas how the alternator tensioner could be the problem? Something when I cranked it and the starter didn't have enough juice?

The car still seems to run fine, its just the dicky idle thats bothering/worrying me. Other ideas?

not completely related but.....my saab had a plastic pulley explode from age and cold temperature. the acc belt was riding on the bolt that held the pulley on. the car had a real hard time idling until i shut it down. are all pulleys present and spinning freely?

Has the battery been completely charged yet? Check the voltage with nothing attached to it.