Erratic idle and squealing on start continuously until car is turned off.

Hello, the warning light you have suggests there is a diagnostic trouble code (or codes) available to be retrieved from the engine's processor. These will provide clues to a technician that will aid in diagnostic testing to find out what is happening to your BMW -- quite likely related to the problems you are having. Separately, the squealing sounds like a drive belt concern - either the belt or a related pulley is showing a concern. Hands on testing is needed. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops