I have a 2006 bmw 330i 125k miles that was having a lot of issues from idling rough and several lights on the dash. When taking it to the mechanic he stated I need to replaced the spark plugs that was causing a misfire on cylinder 4&5 and also the alternator look to be faulty due to a high voltage output. He performed the service and when returned the car ran great for about 2 days then started to die when coming to a stop. When returning he stated that the additional ac voltage is still in my system and would take me to drive it until it bled off? There are no codes but the car tends to shift weird now and also dies like stated before so Is what he saying true a bad alternator could cause excess ac voltage to stay in my system until it bleeds it off. I would think the grounding in the vehicle would dissipate it immediately.
Sounds like nonsense to me. The only place current would be stored (other than the battery) with the engine not running would be capacitors and that would be DC. The only thing that would generate AC current would be a faulty alternator and that would be gone the moment the engine stopped or the faulty alternator was replaced. (Feeding AC into the car's electrical system could do some damage though.) The story of previously generated AC needing to "bleed off" just doesn't pass the smell test.
