Car starts but the RPMs fluctuates and backfiring?

It sounds like the engine needs a tune up, I would also run the codes as well. Here is the instructions on how to swap the plugs out which I would replace the ignition coils as well. Here is a guide that will help.

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

NGK Double Platinum Tipped

Standard Type .................... PLFR5A-11
Cold Type .................... PLFR6A-11
Hot Type .................... PLFR4A-11

https://www.2carpros.com/articles/how-to-change-spark-plugs

Check out the images (below). Please let us know what happens.