I have a 85 eagle Talon TSi and recently I left my lights on and ask my buddie for a boost. After we got the cable connected everyone in and out of my car turned on but I did not physically turned anything on. We thought that was wierd and so I tried to start my car and nothing happened. After going to get a new battery my car started but was idling up and down constant between 1,200 rpm and 2,100. I think its my computer. I can drive it for about 5 min with only driving capabilities on, no sounds from my deck, a/c, lights, nothing. Then after about 20 min of driving my car completely shuts down and then its not drivable until my battery gets charged. Please help me in finding the problem so I can drive my car.

 

sounds like a bad Alternator