Unstable idling and black smoke

Black smoke is caused by excess fuel in the exhaust. Unstable idle and a flashing check engine light is caused by this as well.

Here is a guide that talks about this:

https://www.2carpros.com/articles/engine-black-smoke

The first step is to check codes. This should tell us which cylinder is the issue. More than likely you have a faulty injector but we need to confirm this first. I would try to refrain from driving it until this is repaired because the flashing light means it is doing damage.

If I may, this guide can help you get the codes:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please run down this guide and report back.