Before storing my car for the winter, it threw a P0069 code, which is related to the MAP sensor. The car would occasionally idle very poorly and, after a few weeks, the car would begin to die almost every time it came to a stop. I had it tuned before storage (and after the problem appeared), and the guys at the shop suggested replacing my MAF sensor, which seemed to help for a bit, but eventually the problem returned and the car was barely drivable. It will cruise on the highway just fine, but as soon as I come to a stop, the oil pressure will drop, the boost gauge will flutter towards 0 psi, and the car will run very poorly until it dies and has to be restarted. The only way to avoid this is to constantly modulate the throttle.

I just took the car out of storage, and the battery had died (Optima red top, stored in the trunk). I knew that the idle problem would still be there, so I had it towed to my dealership and they said that the battery had a dead cell, and that that was the cause of my idle issue (inconsistent voltage). They replaced the battery, and I drove the car home today. There's no more CEL, but the car still performs the same, and will die at every stop. Any ideas? This is getting very frustrating!

Thanks