1997 Mazda 626 Car idles low and then shuts off

I recently have had a problem with my car idling..Every time I am in park or sitting somewhere my car Idles really low and it begins to shake..Sometimes it will gain RPMS but sometimes it shuts off.. A few times I will be turning right and it will shut off. I just got a new battery put in and I had them check my altenator..They said it should be putting out about 80 amps but mine is putting out 18 amps..I bought a new one and need to install it..Could that be part of my problem..Im trying to fix it before I drive home 900 miles this coming weekend..Thank you