Just to eliminate some causes here, you are using premium gas right? You need to use at least 91 octane or you’re begging for problems.
Did you check for vacuum leaks?
Also, are you sure it is missing? And not just vibrating, because I’m a little lost on how a car could badly “miss” and idle normally. If it is simply shaking at idle, you probably have a bad motor mount.
Beyond all that, you really need to get your car scanned for codes. Otherwise this is going to take a long time to fix. You can buy a scanner for like $50, or you can take it to Autozone and they will scan it for free.
