1. My car generally doesn't idle that well (jumps around from like 500 to 1000). I think the problem may just be the IAC is dirty.

2. BUT, the car will also stall if a large load is placed on the alt (like holding down the window switch for a few seconds after the windows are already all the way down). Is this the IAC as well, or is something else wrong?

Note: My voltage gauge also jumps around a bit when the blinkers are on. Normal? Or bad alt?

 

Check/clean all involved electrical connections first.

 

if your car is idling at too low a speed then your alternator cant charge fast enough, if that's not the issue then you should take your alternator to NAPA or Advanced Auto and have it tested.

 

What connections are you talking about? Battery terminals and alt? Because it doesn't matter what turns on - headlights, windows, flashers, they all cause the RPM's to go down, and then shoot up to like 1000.