1992 Buick Skylark

Engine Performance problem
1992 Buick Skylark 6 cyl Automatic 70,000 miles

I start her up and after 5 minutes the rpm needle and the battery needle start jumping all over the place like its getting reved up replaced the thermostat for over heating problem now it is doing all this and the battery makes a snapping sound when its started up could the jumping around of the rpm and battery needle be because of the battery being low maybe or is it the IAC valve I am a mom and ive been a back yard mechanic for my entire motherhood and this is the worst time I have had fixing a car I turn 50 next week haha maybe its age related thanks for all the help from all the good guys in here
February 15, 2009.

If you hear a snaping near the battery, there is a loose or bad connection. Make sure the terminals are tight and clean and the ground to the block is too.

Let me know what you find.