Ok so I have a Volvo s40 t5 and when I'm just sitting in my car while it's on it just turns off! But it turns back on instantly, and once it did that it accelerated. Which was scary because it'd never done that before. I have already taken it to get it fixed and it's still doing it. I need help. I do have a video of what it's doing but I don't know how to upload.

 

Welcome to Volvo Forums Lynette

I haven't done video so I'm no help.

Did the shop you took it to think they fixed the problem and if so what is it they did and or replaced ?? Did they mention cleaning the idle air control (IAC) ??
Are you saying it still just dies but you can restart it easily but then the RPMs rev way up ??