Rep Power: 0

My sons car had some mysterious problem where it would not run full power and it has been parked for about 3 months now. I thought from the description he gave that it sounded like the car was running in limp mode before being parked about four months ago. What I found on YouTube sounded like an ECM or ECU problem. But he did not see erratic tachometer or other dash symptoms that were noted in several YouTube posts about this issue. So the car has been parted for a three months now. Today I went through some basic checks. The battery is dead, reading like 2V. The neg terminal connection was found slightly loose so I fixed the connection and checked good continuity to ground good. I check FI ECU fuse under the hood and, it was good. The alternator and battery were replaced about 18 months ago but the car ran fine for months after that. We jump started and the car and it started right up and ran with smooth idle for about 4-5 minutes and then just stopped running. He tried to restart but the battery was still essentially dead and we heard some clicks and the tachometer and spedometer needles bounce once off the bottom once. So we jumped it again and it started right up. I check voltage at the battery terminals and was getting between 12.9 to 13.5 volts, so I think the alternator is working. The car ran for 2-3 minutes this time with smooth idle, reved it a few times and it seemed to be running okay. I check the turn signal an the car stopped running. We jump started it one more time and it ran for a minute and stopped without doing anything. We tried to jump it again and nothing, it will not crank. All the lights on dash came on when key was turned but car would not turn over. Never had time to check for any codes or of even put the car in gear to check for the original issue.

 
Rep Power: 367

check if alternator bolts are loose
change battery