I have a 2003 Chevy Impala. The car will not stay running when idling. It will also shut off quite often when it is deaccelerating. It starts up now problem. I have no check engine lights on, and I had it put on a diagnostic machine but no codes came up. Recent repairs to the vehicle include a new alternator, new serpentine belt, and new tensioner. This issue began shortly after an oil change, however there were no issues detected during the time of the oil change. Any ideas?