Changed the battery now the 2004 XL7 won't idle right It dies when in idle why?

most probably because the computer lost its memory try to take it for a good 15-20 min ride should be ok.

The computer loses it's memory when it is disconnected from the battery for any amount of time. Part of this is the engine idle. The fastest way to "cure" this (takes about 5 mins) is to start it up and give it enough gas to keep it running. Then let off the gas so that it ALMOST stalls and give it a little more gas to keep it running. Repeat about 5-10 times (you will notice it improving). You will need to do this with the AC on and with it off as the idle requirements are different. This worked great in my standard transmission. In the automatic, it's possible you may need to also do the same while it is in the various gears. It's a FAST fix though!