Flashing check engine light, codes P0300 and P0507, engine rattle noise

P0300 is a random multiple misfires and the P0507 is a high idle speed. The common cause for both of those could be a vacuum leak.
Try this guide to see if you can find it:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

You will want to look at all the vacuum lines and fittings as well as the brake booster for the leak. The plastic pieces get brittle and the rubber lines rot from the heat and fluids under the hood.